Network interconnection apparatus, network node apparatus, and packet transfer method for high speed, large capacity inter-network communication

ABSTRACT

A packet transfer scheme in a network system capable of realizing a high speed, large capacity inter-network communication under an internet environment. A network interconnection apparatus (router) has a memory for storing a correspondence relationship between a virtual connection used in receiving a packet from one logical network and a virtual connection used in transmitting a packet to another logical network, and a transfer at a datalink layer is carried out according to the registered correspondence relationship, to effectively form a bypass pipe capable of transferring a packet by an datalink layer level processing alone over a plurality of networks from the transmission terminal to the destination terminal, so that a high speed packet transfer between networks can be realized.

This application is a continuation of application Ser. No. 08/522,115,filed Aug. 31, 1995, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a network interconnection apparatus, anetwork node apparatus, and a packet transfer method suitable for aninternet environment formed by connection-oriented networks.

2. Description of the Background Art

In recent years, due to increasing demands for a variety ofcommunications such as an image communication and a high speed datacommunication, there is an eager expectation for a realization of aB-ISDN (Broadband-Integrated Service Digital Network) in order toprovide highly efficient and flexible communication services, and an ATM(Asynchronous Transfer Mode) exchange scheme is considered as aprospective scheme for actually realizing the B-ISDN. This ATM exchangescheme is a scheme for realizing a communication service by loading datainto a fixed length packet, called a cell, regardless of the attributesof the data, and using this cell as a unit of exchange. The ATMcommunication technique is now studied extensively as a platform forrealizing multi-media communication and high speed, large capacitycommunication, in a field of the public network (B-ISDN) as well as in afield of the LAN (Local Area Network).

Now, in the conventional LAN environment such as that of the Ethernet,the inter-LAN connection, i.e., the inter-networking among the LANs, hasbeen realized by providing a router between each adjacent LANs. The mainfunction of his router is the routing processing for datagramransmission over the LANs, by processing up to the layer 3 (networklayer) in the OSI (Open System Interconnection) protocol layer stack.Namely, for the datagram to be transmitted over two LANs, the datagrammust be brought up to the layer 3 by the router to analyze thedestination network layer address there, and then delivered to thedestination LAN according to the result of this analysis. Here, itshould be noted that, this "router" is often also referred as "gate-way"in the field of the computer communication, but a term "gate-way" isformally defined as an element which carries out the processing up tothe layer 7 in the OSI, so that "gate-way" is actually different fromthe "router", strictly speaking.

There is also an element called a "bridge" which has a similar functionas the router in realizing the inter-LAN connection. In this bridge, incontrast to the router which determines the destination LAN by analyzingthe destination network layer address, the destination LAN is determinedby analyzing the datalink layer address (MAC address). Namely, thebridge realizes the inter-LAN connection by analyzing the destinationMAC address of the datagram and passing the datagram through to anotherLAN when the obtained MAC address is not destined within its own LAN.Thus, in the bridge, only the filtering of data is carried out and thefunctions of the network layer are not realized.

Furthermore, there is also a similar element called a "brouter" whichhas the function of the router as well as the function of the bridge.Namely, this brouter functions as the router for a predetermined networklayer protocol and as the bridge for all the other protocols. In otherwords, in the brouter, those that can be handled by the router are allhandled by the router function, while those that cannot be handled bythe router are handled by the bridge function.

The function of the router, bridge, or brouter has been usually realizedby a workstation (WS). Namely, the function of the router, bridge, orbrouter has been realized as a CPU provided within the WS carries outthe address analysis and transmits the datagram to the allocatedphysical port.

Now, one of the features of the ATM communication scheme is its highspeed operation realized by the hardware switching of the ATM cells.That is, in the ATM communication scheme, the virtual connection (VC) orthe virtual path (VP) is set up end-to-end, while the data to beexchanged end-to-end is loaded in the payload section of the ATM cell,and the ATM cell is exchanged and transmitted up to the destinationterminal by the hardware switching operation alone without theintervention of the software operation, where the hardware switchingoperation is carried out by the ATM switch according to the VPI/VCI(Virtual Path Identifier/Virtual Channel Identifier) or the value ofanother field, such as PT in the ATM cell header, which is contained inthe ATM cell header.

From this point of view, the ATM communication scheme can be consideredas a communication scheme which achieves its high speed operation byreferring only to the ATM cell headers, setting up the virtualconnections/paths end-to-end according to the ATM cell header values,and carrying out the hardware switching. In a case of applying this ATMcommunication scheme to the LAN, it is considered that thecommunications between the terminals in the LAN are realized by thecommunications through the ATM-VC/ATM-VP as described above, and it ispossible to expect a drastic speed up and capacity increase for thecommunications between the terminals.

However, in a case of an ATM-LAN, when inter-LAN communication is to becarried out, the network layer transfer is carried out at the routerbetween the LANs, so that the inter-LAN communication has a problem inthat the speed and the capacity of the communication can be considerablylowered compared with the communication within the LAN. In addition, dueto the processing overhead at the network, there has also been a problemthat the probability for the occurrence of congestion becomes high as aresult of the lowering of the transfer speed and the limitation of theprocessing speed.

On the other hand, the inter-networking scheme used in the conventionaldata network is a connection-less scheme, in which the data unit(network layer service data unit) transmitted to the router by using thedatalink is applied with the OSI layer 3 processing at the router, andthen the relaying of the data unit is carried out. As described above,the bridge for carrying out the filtering of the data unit of thedatalink layer only carries out the filtering of the data unit and thefunctions of the network layer are not realized.

Recently, there are propositions for performing inter-networking notonly in the connection-less mode but also in the connection-orientedmode as well. In short, these propositions introduce the concept of theconnection into the inter-networking at the datalink level or theinter-networking at the network layer level. The ATM is a prime exampleof the former type, while the ST-II recently proposed as theconnection-oriented network layer protocol is an example of the lattertype.

In the ATM, the reservation of the communication resource is made at thedatalink level, while in the ST-II, the reservation of the communicationresource is made at the network layer level. In either case, the set upof the connection is carried out before the communication, so that theyare basically connection-oriented schemes. Here, for the connection-lesscommunication, the processing of the network layer is carried out at theserver (CLS, router, etc.) of the connection-less communication, whereasfor the connection-oriented communication, a header informationrewriting table necessary for the reservation of the communicationresource and the relaying is set up before the start of thecommunication, and then the actual data transfer is handled by therelaying at the datalink level.

However, the currently available usual applications realize theconnection-oriented communication on the connection-less service, suchthat the data unit is transferred by using the connection-lesscommunication mode even for the connection-oriented communication. Inthe connection-less mode, a plurality of processings of the networklayer are carried out, and it is common to re-construct the data unit ofthe network layer in this case. Consequently, even in the applicationwhich is designed to realize a high speed communication by carrying outthe relaying at the datalink level, there has been a problem that theprobability for the occurrence of the congestion becomes high as aresult of the lowering of the transfer speed and the limitation of theprocessing speed due to the processing overhead at the network.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a networkinterconnection apparatus, a network node apparatus, and a packettransfer method, capable of realizing a high speed, large capacityinter-network communication under an internet environment in which aplurality of networks are inter-networked.

According to one aspect of the present invention there is provided anetwork interconnection apparatus for connecting at least two virtualconnection-oriented logical networks, comprising: physical interfacemeans for interfacing the logical networks; first transfer means forapplying a network layer level processing to a packet received from onelogical network and transmitting the packet to another logical network;memory means for storing a correspondence relationship between a virtualconnection used in receiving a packet from said one logical network anda virtual connection used in transmitting the packet to said anotherlogical network; second transfer means for carrying out a packettransfer without the network layer level processing, according to thecorrespondence relationship stored in the memory means; and registrationmeans for receiving a control message containing information for aregistration of the correspondence relationship from at least one of thelogical networks, and registering the correspondence relationship intothe memory means according to the control message.

This aspect of the present invention defines a first configuration of arouter (network interconnection apparatus) according to the presentinvention. In transferring a data packet from a transmission terminalbelonging to one logical network to a destination terminal belonging toanother logical network, this data packet passes through a routerconnecting these logical networks. A conventional router has a ratherslow transfer speed as it transmits a packet received from one logicalnetwork to another logical network by applying a network layer levelprocessing. In contrast, a router of the present invention has memorymeans for storing a correspondence relationship between a virtualconnection used in receiving a packet from one logical network and avirtual connection used in transmitting a packet to another logicalnetwork, and a necessary correspondence relationship is registered intothis memory means according to an explicit control message received fromone logical network. Then, a transfer at a datalink layer is carried outaccording to the registered correspondence relationship, to effectivelyform a bypass pipe capable of transferring a packet by a datalink layerlevel processing alone over a plurality of networks from thetransmission terminal to the destination terminal, so that a high speedpacket transfer between networks can be realized.

In the router of the present invention, when a packet is received fromone logical network, if the correspondence relationship for a virtualconnection used in receiving this packet is in the memory means, thepacket is transferred to another logical network by the second transfermeans for carrying out a transfer processing at a datalink layer levelalone, whereas otherwise the packet is transferred to another logicalnetwork by the first transfer means for carrying out a transferprocessing at a network layer level.

Alternatively, it is also possible to provide additional informationregarding whether a transfer by the first transfer means is to becarried out for a virtual connection used in receiving the packet fromone logical network, such that the transfer by the first transfer meansis carried out if this additional information indicates that thetransfer by the first transfer means is to be carried out for a virtualconnection used in receiving this packet, whereas otherwise the transferby the second transfer means is carried out according to thecorrespondence relationship stored in the memory means.

According to another aspect of the present invention there is provided anetwork node apparatus directly connected with one virtualconnection-oriented logical network, for transmitting packets to a nodeconnected with another virtual connection-oriented logical network,comprising: physical interface means for interfacing the logicalnetworks; memory means for storing a correspondence between adestination node information for each packet to be transmitted and avirtual connection to be used in transmitting each packet; firsttransmission means for transmitting the packet according to thecorrespondence stored in the memory means; and second transmission meansfor transmitting a control message to a network interconnectionapparatus connecting said one logical network and said another logicalnetwork, the control message containing information for a registrationof a correspondence relationship between a first virtual connection usedin receiving a packet from said one logical network and a second virtualconnection used in transmitting the packet to said another logicalnetwork.

This aspect of the present invention defines a configuration of anetwork node (encompassing a terminal as well as an intermediate stagerouter) according to the present invention. The network node whichtransmits a packet to the router has memory means for storing acorrespondence relationship between a destination node information ofthe packet and a virtual connection to be used in transmitting thepacket, and updates this memory means after the control message istransmitted, so that an initial setting to transfer the packet to thedestination node by the transfer processing at a network layer level inthe router can be switched to a setting to transfer the packet to thedestination node by the transfer processing at a datalink layer levelalone, i.e., a bypass pipe, in the router.

Here, the control message can contain an information for specifyingsource and destination nodes of each packet to be transmitted. As anexample, a globally unique bypass pipe ID can be used.

Also, the update of the memory means at the network node can be carriedout at a time of transmitting the control message, or at a time ofreceiving a response message from the router notifying a set up of thebypass pipe.

Also, in a case of using an identical virtual connection for atransmission of the control message and a transmission of a packet suchthat the router registers the correspondence relationship by regardingthis virtual connection used in receiving the control message as avirtual connection used in receiving the packet, the switching from thefirst transfer means to the second transfer means is going to be made atthe router even when the update of the memory means at the transmissionterminal side is not carried out.

According to another aspect of the present invention there is provided amethod of packet transfer for transferring a packet transmitted from afirst node belonging to one logical network to a second node belongingto another logical network, comprising the steps of: determining acorrespondence relationship between a virtual connection available fortransmitting the packet from the first node and a virtual connectionavailable for transmitting the packet to the second node, according to acontrol message containing an identification information for a desiredvirtual connection available for transmitting the packet without anetwork layer level processing over different logical networks, thecontrol message being transmitted from at least one of the first andsecond nodes; storing the correspondence relationship determined at thedetermining step in a memory; and transferring a newly received packetwithout carrying out a network layer level analysis according to thecorrespondence relationship when the correspondence relationship for avirtual connection used in receiving the newly received packet is storedin the memory.

This aspect of the present invention defines a method for forming abypass pipe by using a control message according to the presentinvention. This method encompasses the following three cases.

The first case (out-band, packet) is that in which the control message(which is a type of packet) contains an identification information(VCID, or VCI when a VP directly connecting neighboring routers isprovided) for a first virtual connection available for transmitting thepacket from one of the first node and the second node to the router, inaddition to the identification information (bypass pipe ID) for thedesired virtual connection, and this control message is transmitted fromsaid one of the first node and the second node to the router through asecond virtual connection different from the first virtual connection.Then, the control message is analyzed at a network layer level, to forma bypass pipe connecting the first virtual connection and a virtualconnection connected to a logical network to which another one of thefirst node and the second node belongs, at the router.

Here, the bypass pipe ID is an identification information unique in anentire network system containing a plurality of logical network, and canbe given by an information specifying a transmission terminal and adestination terminal for example. On the other hand, the VCID, or VCIwhen a VP directly connecting neighboring routers is provided, is anidentification information unique within a logical network to which thetransmission terminal belongs.

The second case (out-band, ATM signaling) is that in which the controlmessage (ATM signaling) contains an identification information (VCID, orVCI when a VP directly connecting neighboring routers is provided) for afirst virtual connection available for transmitting the packet from oneof the first node and the second node to the router, which is a usualpart of the ATM signaling message, in addition to the identificationinformation (bypass pipe ID) for the desired virtual connection, andthis control message is transmitted from said one of the first node andthe second node to the router through a virtual connection for an ATMsignaling which is different from the first virtual connection. Then, anATM signaling processing is applied to the control message, to form abypass pipe connecting the first virtual connection and a virtualconnection connected to a logical network to which another one of thefirst node and the second node belongs, at the router.

The third case (in-band) is that in which the control message (which isa type of packet) contains the identification information (bypass pipeID) for the desired virtual connection, and this control message istransmitted from one of the first node and the second node to the routerthrough one virtual connection. Then, a bypass pipe connecting said onevirtual connection and a virtual connection connected to a logicalnetwork to which another one of the first node and the second nodebelongs is formed at the router.

According to another aspect of the present invention there is provided anetwork interconnection apparatus for connecting at least two virtualconnection-oriented logical networks, comprising: physical interfacemeans for interfacing the logical networks; first transfer means forapplying a network layer level processing to a packet received from onelogical network and transmitting the packet to another logical network;memory means for storing a correspondence relationship between a virtualconnection used in receiving the packet from said one logical networkand a virtual connection used in transmitting the packet to said anotherlogical network; second transfer means for carrying out a packettransfer without the network layer level processing, according to thecorrespondence relationship stored in the memory means; and means fordetecting a virtual connection used in receiving the packet and avirtual connection used in transmitting the packet at a time of a packettransfer by the first transfer means, and registering the correspondencerelationship into the memory means according to the detected virtualconnections.

This aspect of the present invention defines a second configuration of arouter (network interconnection apparatus) according to the presentinvention. Here, just as in the first configuration described above,this router forms a bypass pipe capable of transferring a packet by adatalink layer level processing alone over a plurality of networks fromthe transmission terminal to the destination terminal, so that a highspeed packet transfer between networks can be realized. The firstconfiguration uses the control message so that it is possible to form abypass pipe in a manner fully accounting for each request from a user oran application, while this second configuration registers the necessarycorrespondence relationship into the memory means according to aninformation on a virtual connection obtained at a time of transferring apacket by applying a network layer level processing, and a transferprocessing is switched from a transfer by a network layer levelprocessing to a transfer by a datalink layer level processing alone oncethe correspondence relationship is registered in the memory means, sothat a bypass pipe for a high speed transfer can be set up without usinga special message.

According to another aspect of the present invention there is provided amethod of packet transfer for transferring a packet transmitted from afirst node belonging to one logical network to a second node belongingto another logical network, comprising the steps of:

receiving a packet containing a destination node information transmittedthrough a first virtual connection available for transmitting the packetfrom the first node;

analyzing the destination node information contained in the packet at anetwork layer level, and determining a second virtual connectionavailable for transmitting the packet to the second node; transmittingthe packet through the second virtual connection, while storing acorrespondence relationship between the first virtual connection used inreceiving the packet and the second virtual connection used intransmitting the packet in a memory; and transferring a newly receivedpacket without carrying out a network layer level analysis according tothe correspondence relationship when the correspondence relationship fora virtual connection used in receiving the newly received packet isstored in the memory.

This aspect of the present invention defines a method for forming abypass pipe without using a control message according to the presentinvention.

Thus, in a case of forming a bypass pipe by using a control message,there is provided a network system, comprising: a plurality of virtualconnection-oriented logical networks; a plurality of network nodesconnected to the logical networks, the nodes include terminal nodes andnetwork interconnection apparatuses interconnecting the logicalnetworks, each network interconnection apparatus has a memory means forstoring a correspondence relationship between a virtual connectionavailable for transmitting a packet from one network node and a virtualconnection available for transmitting the packet to another networknode, and each network interconnection apparatus transfers a newlyreceived packet without carrying out a network layer level analysis whena correspondence relationship for a virtual connection used in receivingthe newly received packet is stored in the memory means, whereas eachnetwork interconnection apparatus transfers the newly received packet bycarrying out the network layer level analysis when the correspondencerelationship for a virtual connection used in receiving the newlyreceived packet is not stored in the memory means; wherein each networknode belonging to one logical network and wishing to transfer the packetto another network node belonging to another logical network transmits acontrol message containing an identification information for a desiredvirtual connection available for transmitting the packet without anetwork layer level processing over different logical networks,according to which each network interconnection apparatus connectedbetween said one logical network and said another logical networkupdates the connection relationship stored in the memory means.

On the other hand, in a case of forming a bypass pipe without using acontrol message, there is provided a network system, comprising: aplurality of virtual connection-oriented logical networks; a pluralityof network nodes connected to the logical networks, the network nodesinclude terminal nodes and network interconnection apparatusesinterconnecting the logical networks, each network interconnectionapparatus has a memory means for storing a correspondence relationshipbetween a first virtual connection available for transmitting a packetfrom one network node and a second virtual connection available fortransmitting the packet to another network node, and each networkinterconnection apparatus transfers a newly received packet withoutcarrying out a network layer level analysis when a correspondencerelationship for a virtual connection used in receiving the newlyreceived packet is stored in the memory means, whereas each networkinterconnection apparatus transfers the newly received packet bycarrying out the network layer level analysis when the correspondencerelationship for a virtual connection used in receiving the newlyreceived packet is not stored in the memory means; wherein when eachnetwork interconnection apparatus receives the newly received packettransmitted through the first virtual connection, each networkinterconnection apparatus analyzes a destination node informationcontained in the newly received packet at a network layer level anddetermine the second virtual connection to update the connectionrelationship stored in the memory means.

It is to be noted that the virtual connection-oriented network hererefers to a network capable of setting a plurality of virtualconnections between a terminal apparatus and a network interconnectionapparatus (router) or between network interconnection apparatuses(routers), and changing a purpose of using each of these virtualconnections, connection by connection. ATM, frame relay, and X.25 areexamples of the virtual connection-oriented network.

Also, a logical network here refers to a network that can be handledlogically as a single entity, regardless of a physical configuration.For example, a logical network is defined by a range sharing anidentical network ID in a certain physical network configuration.

On the other hand, a packet here refers to a packet of a network layeras well as a packet of a datalink layer such as an ATM cell, an Ethernetframe, an AAL PDU (ATM Adaptation Layer Protocol Data Unit), etc.

Other features and advantages of the present invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing an overall configuration ofone embodiment of an ATM network according to the present invention.

FIG. 2 is a schematic block diagram showing an internal configuration ofeach ATM-LAN in the ATM network of FIG. 1.

FIG. 3 is a diagrammatic illustration of a routing table provided ineach ATM switch node in the ATM-LAN of FIG. 2.

FIG. 4 is a block diagram showing a configuration of each router in theATM network of FIG. 1.

FIG. 5 is a block diagram showing a configuration of a 2 port router tcan be used as each router in the ATM network of FIG. 1.

FIG. 6 is a block diagram showing a physical internal configuration of ageneral purpose computer implementing the 2 port router of FIG. 5.

FIG. 7 is a flow chart showing a procedure for packet transfer by therouter of FIG. 4.

FIG. 8 is a diagrammatic illustration of an L3 routing table that can beprovided in the router of FIG. 4.

FIG. 9 is a block diagram showing a configuration of each transmissionterminal in the ATM network of FIG. 1.

FIG. 10 is a diagrammatic illustration of a VC management table contentused in the transmission terminal of FIG. 9.

FIG. 11 is a diagrammatic illustration of a destination management tablecontent used in the transmission terminal of FIG. 9.

FIG. 12 is a flow chart showing a procedure for transmitting a datapacket by the transmission terminal of FIG. 9.

FIG. 13 is a diagram showing possible outlines of a procedure for setup/release of a bypass pipe using a hard state scheme in the ATM networkof FIG. 1.

FIG. 14 is a diagram showing a detailed control message sequence to beused at a time of bypass pipe set up in one case.

FIG. 15 is a diagram showing a detailed control message sequence to beused at a time of bypass pipe set up in another case.

FIG. 16 is a diagram showing a detailed control message sequence to beused at a time of bypass pipe set up in still another case.

FIG. 17 a table summarizing operations of the router in the controlmessage sequences FIGS. 14 to 16 and FIGS. 19 to 21.

FIGS. 18A, 18B, 18C, 18D, and 18E are diagrammatic illustrations of a VCmanagement table, an available VC table, a bypass pipe management table,an IP-VC correspondence table, and an IP routing table, respectively,which are used by the operations of the router summarized in FIG. 17.

FIG. 19 is a diagram showing a detailed control message sequence to beused at a time of bypass pipe release in on case.

FIG. 20 is a diagram showing a detailed control message sequence to beused at a time of bypass pipe release in another case.

FIG. 21 is a diagram showing a detailed control message sequence to beused at a time of bypass pipe release in still another case.

FIG. 22 is a state transition diagram summarizing procedures andinternal operations for bypass pipe set up and release using a hardstate scheme in the ATM network of FIG. 1.

FIG. 23 is a flow chart showing an operation of one router in anexemplary bypass pipe set up procedure using control message exchanges.

FIG. 24 is a flow chart showing an operation of another router in anexemplary bypass pipe set up procedure using control message exchanges.

FIG. 25 is a schematic block diagram showing an exemplary situation usedin explaining an exemplary bypass pipe set up procedure using controlmessage exchanges.

FIG. 26 is a diagram showing possible outlines of a procedure for setup/release of a bypass pipe using a soft state scheme in the ATM networkof FIG. 1.

FIG. 27 is a state transition diagram summarizing procedures andinternal operations for bypass pipe set up and release using a receiverinitiative soft state scheme in the ATM network of FIG. 1.

FIG. 28 is a table summarizing operations of the router in the procedurefor set up/release of a bypass pipe using a receiver initiative softstate scheme.

FIG. 29 is a state transition diagram summarizing procedures andinternal operations for bypass pipe set up and release using a senderinitiative soft state scheme in the ATM network of FIG. 1.

FIG. 30 is a table summarizing operations of the router in the procedurefor set up/release of a bypass pipe using a sender initiative soft statescheme.

FIG. 31 is a flow chart showing an operation of a router in the ATMnetwork of FIG. 1 in a case of a change in the rout table due to therouting protocol operation.

FIG. 32 is a diagram showing an outline of a procedure for setting up abypass pipe using a in-band scheme in the ATM network o FIG. 1.

FIG. 33 is a flow chart showing an operation of one router in one methodfor a bypass pipe set up in a case of using SVC.

FIG. 34 is a flow chart showing an operation of another router in onemethod for a bypass pipe set up in a case of using VC.

FIG. 35 is a diagram showing possible control message sequences inanther method for a bypass pipe set up/release in a case of using SVC.

FIG. 36 is a schematic block diagram showing an exemplary configurationfor the ATM network of FIG. 1.

FIG. 37 is a flow chart showing an operation at a time of starting thebypass pipe set up procedure in a case of using a statisticalinformation.

FIG. 38 is a flow chart showing an operation at a time of starting thebypass pipe set up procedure in a case of using a router activationtiming.

FIG. 39 is a flow chart showing an operation at a time of starting thebypass pipe set up procedure in a case of using a packet transmissiontiming.

FIG. 40 is a flow chart showing an operation of one router in one bypasspipe set up procedure using no control message.

FIG. 41 is a flow chart showing an operation of another router in onebypass pipe set up procedure using no control message

FIG. 42 is a schematic block diagram showing another exemplaryconfiguration for the ATM network of FIG. 1 for explaining anotherbypass pipe set up/release procedure using no control message.

FIG. 43 is a block diagram showing a configuration of each terminal theexemplary configuration of FIG. 42.

FIG. 44 is a block diagram showing a configuration of each router in theexemplary configuration of FIG. 42.

FIGS. 45A, 45B, 45C, 45D, and 45E are diagrammatic illustrations ofrouter control tables provided in switches in the exemplaryconfiguration of FIG. 42.

FIGS. 46A, 46B, 46C, and 46D are diagrammatic illustrations of VCmanagement tables provided in a host H1, a host H2, a router A, androuter B, respectively, in the exemplary figuration of FIG. 42.

FIG. 47 is a flow chart showing a procedure for data packet transmissionby a transmission terminal in the exemplary configuration of FIG. 42.

FIG. 48 is a flow chart showing a procedure for data packet handling bya router in the exemplary configuration of FIG. 42.

FIG. 49 is a diagrammatic illustration of a VC management table contentfor still another bypass pipe set up/release procedure using no controlmessage.

FIG. 50 is a flow chart showing a procedure for data packet transmissionby a transmission terminal in a procedure using the VC management tablecontent of FIG. 49.

FIG. 51 is a flow chart showing a procedure for data packet handling bya router in a procedure using the VC management table content of FIG.49.

FIG. 52 is a schematic block diagram showing still another exemplaryconfiguration for the ATM network of FIG. 1 for explaining a bypass pipeset up procedure for a multi-point to point connection.

FIG. 53 is a flow chart showing an operation of one router in a bypasspipe set up procedure for a multi-point to point connection.

FIG. 54 is a schematic block diagram showing exemplary connections amongsome routers in the still another exemplary configuration of FIG. 52.

FIG. 55 is a schematic block diagram showing an exemplary multi-point topoint connection among some routers in the still another exemplaryconfiguration of FIG. 52.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the preferred embodiment in a form of an ATM network incorporatinga network interconnection apparatus, a network node apparatus, and apacket transfer method according to the present invention will bedescribed in detail.

CONFIGURATION OF ATM-LAN

The ATM network of this embodiment has an overall configuration of anATM internet as shown in FIG. 1, which comprises ATM-LANs 603 andEthernets 600 interconnected by routers 601, and Hosts 602 connected tothe ATM-LANs 603 or the Ethernets 600.

Here, the ATM-LAN 603 is a local area network operated by the ATMscheme, and this ATM-LAN 603 may very well be operated according to theprotocol defined by the standardizing organization such as the ATMforum, for example. The router 601 is a device for mutually connecting aplurality of LANs (ATM-LANs in this embodiment). The Host 602 is adevice for carrying out transmission and reception of packets.

In this ATM internet configuration of FIG. 1, the ATM-LAN 603 functionsas a sub-net of the IP (Internet Protocol) so that each ATM-LAN 603 hasa sub-net address (sub-net ID). In the following, only an exemplary caseof using IP/IP address as network layer protocol/network layer addressconstituting the ATM internet will be described, but the similardescription is also possible for the other protocols such asnetware/IPX, AppleTalk, etc. Also, in the following description, a term"sub-net" is intended to imply "logical network in the network layer".

It should be apparent from the foregoing description that thisembodiment deals with a case in which the physical LAN (ATM-LAN) and thelogical sub-net (IP sub-net) coincide with each other, that is, a casein which each ATM-LAN corresponds to one sub-net. Here, however, thesimilar description is also possible for a case in which a plurality ofsub-nets are logically constructed within one ATM-LAN, assuming that therouter provides support (of the network management, the datagramtransmission, etc.) for these plurality of sub-nets as well.

Next, an exemplary internal configuration of the ATM-LAN 603 is shown inFIG. 2, which comprises mutually connected ATM switch nodes 21 to 24 andterminal devices 2A to 2G connected to the ATM switch nodes 21 to 24.

Each of the ATM switch nodes 21 to 24 is a switching hub which containsa built-in ATM switch (or device having an equivalent function as an ATMswitch) therein, and which has a plurality of ports through which it isconnected with the terminal devices or the other ATM switch nodes. Inthis embodiment, it is assumed that the connection interface among themis the ATM scheme. Each of these nodes has a routing table in a formshown in FIG. 3 in which an interface and a corresponding VPI/VCI arespecified for the input side and the output side such that the datatransfer can be carried out according to this table.

Each of the terminal devices 2A to 2G is a device such as a personalcomputer (PC), a workstation (WS), a printer, a server, etc., which hasan ATM interface (or a terminal adaptor having an ATM interface) fordirect connection with the ATM-LAN.

Each ATM-LAN 603 in FIG. 1 has this type of an internal configurationformed by the ATM switch nodes and the terminal devices, but factorssuch as a topology among the internal ATM switch nodes, a connectioninterface speed, a number of nodes, a number of terminals, etc. arearbitrary in each ATM-LAN.

This ATM-LAN 603, which is an LAN in accordance with the ATM forum forexample, has the following features.

(1) Each terminal device or ATM switch node has its own link layeraddress (ATM address in this embodiment). Here the link layer addressesdo not overlap with each other within one ATM-LAN.

(2) Each terminal device or ATM switch node has its own IP address asthe network layer address, where the network layer address is a globallyunique address in general.

(3) Each terminal device or ATM switch node has a broadcast channel withrespect to the ATM-LAN to which it belongs, such that each terminaldevice or ATM switch node can transmit a message (cell) simultaneouslyto all the other terminals/nodes belonging to that ATM-LAN through thebroadcast channel.

Each ATM-LAN also has a VPI/VCI value determination function (not shown)provided therein which has a right to determine the VPI/VCI values to beused within each ATM-LAN, which is an independent right in each ATM-LAN.Whenever there is data to be transmitted, the terminal device or node inthe ATM-LAN loads that data into an ATM cell, attaches a prescribed ATMcell header, and transmits that ATM cell in that ATM-LAN, regardless ofwhether the transmission destination is within that ATM-LAN.

Now, some terms to be used in this embodiment will be defined.

A network layer level indicates a basic unit of transfer through thenetwork, which is a layer for handling the routing control, etc. Anaddress to be used in the transfer or the routing control at the networklayer will be referred as a network layer address.

A host is a device other than the router which transmits and receivespackets of the network layer level, such as a terminal device, forinstance.

A node is a generic name indicating the router and the host.

Neighboring routers are routers that can directly transmit the packetsof the network layer level with one another, without being intermediatedby the other routers.

A VCID (VC IDentifier) is an identifier for identifying a virtualconnection (VC), which is identical between the host and the router, aswell as between the neighboring routers. In a case of the ATM, acorrespondence relationship between the VCID and VPI/VCI is stored ateach host and router. The VCID is unique within a range in which the VCis set up (which is within the ATM network in this embodiment).

A dedicated VC is a VC to be set up between the host and the router orbetween the neighboring routers, which is used at a time of forming abypass pipe.

A default VC is a VC to be set up between the host and the router orbetween the neighboring routers, which is used at a time of transferringthe packet hop by hop.

A bypass pipe is a connection formed by connecting a plurality ofdedicated VCs, which provides a mechanism for sending the data packetfrom a transmitting terminal to a receiving terminal by using only alower level packet transfer unit, without passing through a packettransfer unit of the network layer level, at a network interconnectionapparatus through which the data packet passes in its course.

CONFIGURATION OF ROUTER

In this embodiment, each router has a configuration as shown in FIG. 4,which comprises: a plurality of network interface units (network I/Funits) 201; a datalink layer switch unit 202 connected with the networkI/F units 201; a datalink layer-network layer translation unit 203connected with the datalink layer switch unit 202; a network layerswitch unit 204 connected with the datalink layer-network layertranslation unit 203; a data link layer connection set up judgement unit205 connected with the network layer switch unit 205; a datalink layercontrol unit 206 connected with the datalink layer switch unit 202, thenetwork layer switch unit 204, and the datalink layer connection set upjudgement unit 205; and a network layer control unit 207 connected withthe network layer switch unit 204.

This router of FIG. 4 is connected with a desired LAN such as theATM-LAN, Ethernet, FDDI, etc., through each network I/F unit 201, and atleast one of the plurality of network I/F units 201 is accommodating avirtual connection-oriented LAN such as the ATM-LAN. Here, the LANs suchas the ATM-LAN, Ethernet, etc. are treated as the datalink layer.

In the following, the datalink layer is also referred as L2, while thenetwork layer is also referred as L3.

The datalink layer switch unit 202 is a unit for determining an outputnetwork I/F unit 201 for a datalink layer frame according to a headeraddress of a datalink layer frame whenever a datalink layer framearrives from the LAN connected with the network I/F unit 201 or from thedatalink layer-network layer translation unit 203. In order to determinethe output network I/F unit 201, this datalink layer switch unit 201 isprovided with a datalink layer routing table (L2 routing table) therein,where this datalink layer routing table is managed by the datalink layercontrol unit 206. By providing this datalink layer switch unit 202, itbecomes possible to carry out a faster packet/cell switching comparedwith a case of using only a network layer switching.

The datalink layer-network layer translation unit 203 carries out atranslation from an L2 frame to an L3 packet, and from an L3 packet toan L2 frame. This corresponds to an AAL in the ATM for instance. Thus,in a case where an ATM cell is entered from the datalink layer switchunit 202, the entered ATM cell is assembled into an L3 packet. Also, ina case where an L3 packet is entered from the network layer switch unit204, the entered L3 packet is disassembled into an ATM cell.

The network layer switch unit 204 has an L3 routing table and a functionsimilar to those of a conventional router, in which a destinationaddress of an L3 packet is checked and compared with the L3 routingtable to determine an output network I/F.

The datalink layer connection set up judgement unit 205 judges theswitching from a network layer transfer in which an output target isdetermined by the network layer switch unit 204 to a datalink layertransfer in which an output target is determined by the datalink layerswitch unit 202, when packets over a prescribed number have beenentered, outputted, or passed according to an input/output statisticsdata for L3 packets, or when there is a notice from an upper protocol.By means of this function, it is possible to realize a high speed packettransfer. Here, the datalink connection can be newly set up by thedatalink layer control unit 206 at a time of switching from the networklayer transfer to the datalink layer transfer, or the datalinkconnections may be set up in advance and an unused datalink connectionis used at a time of switching from the network layer transfer to thedatalink layer transfer. A method for judging the switching in thisdatalink layer connection set up judgement unit 205 will be described indetail later.

The datalink layer control unit 206 carries out a set up/release of aconnection, and a relaying of packets for the sake of connection setup/release, in a case where the datalink layer is a connection orientedone such as the ATM. Here, connection information for connections set upor released by this datalink layer control unit 206 is registered ordeleted in the L2 routing table provided in the datalink layer switchunit 202.

The network layer control unit 207 has a function for managing the L3routing table provided in the network layer switch unit 204. In a casewhere the L3 routing table is static, the L3 routing table is set uponly once at the beginning. In a case of a dynamic routing, the routinginformation is exchanged with neighboring routers in order to manage theL3 routing table. The routing information exchange among the neighboringrouters can be realized by using the existing routing protocol such asRIP (Routing Information Protocol), OSPF (Open Shortest Path First),etc.

Next, the router having physical interfaces with respect to two ATM-LANswill be described as an exemplary case of the router of this embodiment.This type of router will be referred as a "2 port router".

The 2 port router has a configuration as shown in FIG. 5, whichlogically comprises: network I/Fs (network interface-A and networkinterface-B) 31 and 33; an add/drop and header conversion unit 32provided between the network I/Fs 31 and 33; an AAL processing unit 34connected with the add/drop and header conversion unit 32; and a networklayer processing unit 35, a datalink layer control unit 36, and a routercontrol unit 37, all of which are connected with the AAL processing unit34.

The network I/Fs 31 and 33 are provided in correspondence to thephysical ports of the router, to function as the physical interfaceswith respect to the ATM-LANs. Each network I/F has functions forcarrying out a conversion processing between a signal on a physicaltransmission medium and an ATM cell, such as E/O conversion, O/Econversion, SDH (Synchronous Digital Hierarchy) processing, cellsynchronization processing, scrambling/descrambling processing, etc. forexample, as well as an exchange of ATM cells with respect to theadd/drop and header conversion unit 32.

The add/drop and header conversion unit 32 corresponds to the datalinklayer switch unit 202 of FIG. 4, and has a function for dropping(extracting) cells having prescribed ATM cell header values (such asVPI/VCI/PT values) among the cells transmitted from the network I/Fs 31and 33 and sending out the dropped cells to the AAL processing unit 34,a function for converting cell headers of cells having prescribed ATMcell header values according to a header conversion table providedtherein and sending out these cells to a network I/F on an opposite side(without sending them to the AAL processing unit 34), and a function foradding (inserting) and sending out the ATM cells handed from the AALprocessing unit 34 into a specified direction. In this add/drop andheader conversion unit 32, in a case where cells having ATM cell headervalues which are not registered in the header conversion table areentered, these cells may be discarded in this module and empty cells maybe inserted and outputted to an output side instead.

The AAL processing unit 34 corresponds to the datalink layer-networklayer translation unit 203 of FIG. 4, and has a function for celldisassembling the ATM cells handed from the add/drop and headerconversion unit 32, assembling the upper layer packets (such as IPpackets), and handing the packets to a processing unit of a destinationupper layer (such as a router processing unit or a router control unitin this embodiment), and a function for cell assembling the packetshanded from a processing unit of an upper layer (such as a routerprocessing unit) and sending them out to the add/drop and headerconversion unit 32.

The network layer processing unit 35 corresponds to the network layerswitch unit 204 and the network layer control unit 207 of FIG. 4, andhas a function of the router for carrying out the network layerprocessing (that is, a function for receiving a datagram (such as an IPdatagram) from the AAL processing unit 34 and carrying out the routingprocessing for this datagram, while carrying out data exchange or dataprocessing for the routing protocol (such as RIP or OSPF) with respectto the other routers), and a function for carrying out data exchange anddata processing for an "ATM internet bypass pipe set up protocol" to bedescribed later, as well as processing necessitated by the processingresult of this protocol by acting on the datalink layer control unit 36and the add/drop and header conversion unit 32.

The datalink layer control unit 36 has a function for carrying outconnection processing for the datalink layer (ATM-LANs in thisembodiment) connected through the network I/Fs 31 and 33, as well as asignaling processing and call processing.

The router control unit 37 has a function for carrying out control ofthe router as a whole, and carries out an initialization of the routeras well.

Now, the router of this embodiment can be constructed by using adedicated device, or by using a general purpose computer such as apersonal computer, or a workstation. Here, a case of constructing the 2port router described above by using a general purpose computer (aworkstation in this embodiment) will be described.

In this case, the 2 port router has a physical internal configuration asshown in FIG. 6, which generally comprises a workstation (WS) 41 and acommunication board 42 connected to the WS 41 as an extension board.Here, the WS 41 has no communication interface in a form of the ATMinterface, and the ATM interface function is provided by thecommunication board 42.

The communication board (ATM communication board) 42 comprises: aphysical interface handling unit-A 421 connected with one physicaltransmission medium through one ATM communication interface; a cellsynchronization unit-A 422 connected with the physical interfacehandling unit-A 421; a physical interface handling unit-B 423 connectedwith another physical transmission medium through another ATMcommunication interface; a cell synchronization unit-B 424 connectedwith the physical interface handling unit-B 423; an add/drop and headerconversion unit 425 connected with the cell synchronization unit 422 andthe cell synchronization unit 424; an AAL processing unit 426 connectedwith the add/drop and header conversion unit 425; and a bus interfaceunit 427 connected with the AAL processing unit 426 and a standard busI/F for interfacing the WS 41 and the communication board 42.

The WS 41 comprises: a CPU 411, a main memory 412, a hard disk (HD) 414,and a bus interface (bus I/F) 413 connected with the CPU 411 and themain memory 412 through a main bus 415 as well as with the HD 414 andthe standard bus I/F through a peripheral bus 416. Here, the other usualelements of the WS 41 such as CRT, frame memory, other networkinterfaces, etc. are omitted in FIG. 6.

Each element of the communication board 42 has the following functions.

Each of the physical interface handling units 421 and 423 has a functionfor carrying out a conversion between the physical transmission medium(such as optical fiber, coaxial cable, shield-less twist pair cable,etc.) and a physical processing scheme within the communication board 42(electric interface in this embodiment). In addition, each physicalinterface handling unit also has a function for adapting thetransmission scheme to the SDH scheme when the physical transmissionmedium uses such an ATM cell transmission scheme, a function fornotifying an abnormality of the physical interface handling unit to theexternal, and registers for initial settings, etc.

Each of the cell synchronization units 422 and 424 has a function fortaking a synchronization in an ATM cell unit by referring to andprocessing an HEC (Header Error Control) field of an ATM cell in the bitstream entered from the physical interface handling unit 421 or 423, anda function for calculating and inserting the HEC field into an ATM celltransmitted from the add/drop and header conversion unit 425.

In the following, an interface formed by the physical interface handlingunit-A 421 and the cell synchronization unit-A 422 will be referred asan A-side interface, while an interface formed by the physical interfacehandling unit-B 422 and the cell synchronization unit-B 424 will bereferred as a B-side interface. These A-side interface and B-sideinterface correspond to the network interface-A 31 and the networkinterface-B 33 of FIG. 5, respectively.

The add/drop and header conversion unit 425 has a function for dropping(extracting) cells having prescribed ATM cell header values (such asVPI/VCI/PT values) among the cells transmitted from the cellsynchronization units 422 and 424 and sending out the dropped cells tothe AAL processing unit 426, a function for converting cell headers ofcells having prescribed ATM cell header values according to a headerconversion table provided therein and sending out these cells to thecell synchronization unit on an opposite side, and a function for adding(inserting) and sending out the ATM cells handed from the AAL processingunit 426 into a specified direction (a cell synchronization unit in aspecified direction). In this add/drop and header conversion unit 425,in a case where cells having ATM cell header values which are notregistered in the header conversion table are entered, these cells arediscarded in this module and empty cells are inserted and outputted toan output side instead.

The AAL processing unit 426 has a function for cell disassembling theATM cells handed from the add/drop and header conversion unit 425,assembling them in forms of the upper layer packets, storing thesepackets, and handing these packets to the bus interface 427 according tothe need, and a function for storing the upper layer packets handed fromthe bus interface 427, ATM cell assembling these packets according tothe need, and sending out these ATM cells to the add/drop and headerconversion unit 425.

The bus interface 427 has a function for interfacing the input/outputdata of the standard bus interface of the WS 41 with respect to thecommunication board 42, and a function for relaying the set up commandsto each module within the communication board 42 from the WS 41 sidegiven through the standard bus interface or the notices from each modulewithin the communication board 42 to the WS 41 side, so as to carry outthe control of each module in the communication board 42.

Next, each element of the WS 41 has the following functions.

The CPU 411 is a main processor of the WS 41, where an operating systemoperable on the WS 41 and various application programs operable on theWS 41 are operated on this CPU 411. In addition, in this embodiment, theconfiguration of FIG. 6 operates as the router, so that the software ofthe application programs for the router are also operated on this CPU411.

Here, the application programs for the router includes:

(1) a control/management program for the router,

(2) a link layer connection control program for setting up, changing,disconnecting, and managing link layer connection (ATM connection)between the router and the link layer network (ATM-LAN) connected to it,

(3) a network layer processing (router processing) program, and

(4) a control program of the communication board 42.

It is to be noted that the link layer connection (2) and a part of thecontrol program of the communication board 42 (4) may be implemented asa device driver of the WS 41 by regarding the communication board 42 asone of the devices for the WS 41.

The main memory 412 is a main data storage device for the WS 41.

The bus interface 413 has a function for electricallyconnecting/disconnecting the main bus 415 and the peripheral bus 416according to commands from the CPU 411.

The hard disk (HD) 414 is a large capacity data memory device connectedto the peripheral bus 416.

The WS 41 has at least one extension slot, and this extension slot hasits own peripheral bus 416 and a corresponding bus (such as S bus, TURBObus, ISA bus, PCI bus, etc.).

Also, it may be possible for the WS 41 of this embodiment to have aconfiguration capable of directly referring to addresses of a memoryprovided in the bus interface unit 427 or in the AAL processing unit 426through the bus interface unit 427 in the communication board 42, viastandard bus interface. Namely, it may be possible for the CPU 411 toregard a memory space within the communication board 42 as a part of theaddress space (or I/O space) directly visible from the CPU 411.

The bus interface unit 427 in the communication board 42 connected withthe WS 41 has a function for carrying out a control of each modulewithin the communication board 42 as described according to commandsfrom the CPU 411. In other words, the CPU 411 carries out varioussettings of each module in the communication board 42 via the businterface unit 427, according to commands from the router softwareoperated on the CPU 411 described above, as follows.

First, the router software operated on the CPU 411 carries out theinitialization of the communication board 42. This initializationincludes the link layer connection processing software, the networkmanagement software, and the router processing software as theinter-networking device software operated on the CPU 411, a function ofconnection set up in the ATM-LAN connected to the router, and anestablishment of the ATM connection/upper layer connection with respectto the other routers, etc. The establishment of the ATM connection isrealized as the router software operated on the CPU 411 sets up thespecific processing contents with respect to the add/drop and headerconversion unit 425 via the bus interface unit 427, such as "those ATMcells which have prescribed ATM cell header values among the ATM cellsentered from a certain physical interface are to be dropped to the WS 41side", "the AAL processing unit 426 is to cell disassemble the droppedATM cells and hand them to the CPU 411 (or the router software providedtherein) through the bus interface unit 427", and "in order to outputdata from the CPU 411 (or the router software provided therein) to theexternal of the WS 41, that data is to be handed to the AAL processingunit 426 through the bus interface unit 427, and ATM cell assembled byattaching the prescribed ATM cell header value there, and then the ATMcell is to be added and outputted to an appropriate physical interfaceside by the add/drop and header conversion 425".

At this point, the data exchange between the WS 41 and the communicationboard 42 may be realized by using a scheme for specifying one of theA-side and B-side physical interfaces from which that data wastransmitted or to which that data is to be transmitted, along with theATM cell header value.

Next, an ATM connection which passes through the router at the ATM layerprocessing alone (which will be referred hereafter as a bypass ATMconnection) will be described.

A set up of a bypass ATM connection to be set over the router is carriedout by various programs operated on the CPU 411. A physical setting ofthe actual bypass ATM connection is made as follows. Namely, thesoftware operated on the CPU 411 sets up the processing content that "anATM cell entered from the physical interface of one side (A-side forinstance) which has a specific ATM cell header value (header value=X forinstance) is to be outputted to another side (B-side for instance) afterthe cell header value is rewritten into a prescribed value (headervalue=Y for instance)", with respect to the add/drop and headerconversion unit 425 through the bus interface unit 427. An appropriatesetting is also made with respect to the add/drop and header conversionunit 425 in a case where there is an ATM connection in an oppositedirection (such as a ATM connection in B→A direction, or a bidirectionalconnection). By means of this, the ATM cell with the header value=Xentered from the A-side for example will be outputted to the B-sideinterface with the cell header value rewritten into the header value=Y.At this point, in the router (i.e., in the communication board), onlythe ATM layer processing is carried out. In this manner, it is possibleto set up a bypass ATM connection which passes through the communicationboard 42 at the ATM layer processing alone.

Here, the add/drop and header conversion unit 425 may be provided with aUPC function, i.e., a policing/shaping function therein. Namely, it ispossible to carry out a cell flow monitoring or a cell flow regulationon the cell flow having specific ATM cell header values.

PROCEDURE FOR PACKET TRANSFER

Next, a procedure for packet transfer by the router in this embodimentas shown in FIG. 4 will be described with reference to the flow chart ofFIG. 7.

When the datalink layer frame is entered from the network I/F unit 201(step S1), the datalink layer switch unit 202 searches through the L2routing table t1 with an input connection ID or L2 destination addressof the received datalink layer frame as a search key (step S2) todetermine the output I/F.

In a case where the search is successful, the received datalink layerframe is handed to the output I/F registered in the searched out entry,while the output connection ID in the packet is rewritten according tothe searched out entry of the L2 routing table (step S6), and thereceived datalink layer frame is outputted from the network I/F unit 201of the determined output I/F (step S13).

On the other hand, when the determined output I/F indicates an upperlayer, or when there is no corresponding entry, the received datalinklayer frame is handed to the datalink layer-network layer translationunit 203 to carry out an assembling of an L3 packet from an L2 frame(step S3). For example, in a case of the ATM, the AAL processing is tobe carried out here, whereas in a case of the Ethernet, the header is tobe removed here. After the translation from the L2 frame to the L3packet is carried out, the network layer switch unit 204 determineswhether this L3 packet is destined to this node or not (step S4), and ifso, the L3 packet destined to this node is handed to the upper layer(the network layer control unit 207, the datalink layer control unit206, and the datalink layer connection is set up judgement unit 205)(step S5). Otherwise, the L3 packet is not destined to this node and isto be transferred, so that the following operation is carried out for atransmission of a packet.

Namely, the network layer switch unit 204 searches through the L3routing table t4 with a destination L3 address of the packet as a searchkey, to determine the next hop L3 address and the output I/F (step S8).Here, the destination L3 address may not necessarily be the destinationaddress to which the packet is to be transferred, and can be any of asource address, a network mask, a flow ID to be set by IPng, anapplication ID such as a TCP/UDP port, etc. By using the network mask,it becomes possible to specify a group of a plurality of hosts ratherthan specifying just one destination host, so as to enable more generaldestination specification. Also, by using the flow ID or the TCP/UDPport, it becomes possible to specify a specific application of thedestination host, so as to enable more detailed destinationspecification. In the following, it is assumed that the destinationaddress is indicated by any one or more of "address of destined host","network mask of destined host", "address of source host", "network maskof source host", "flow ID", and "transport layer port (such as TCP/UDPport)".

When the output I/F is determined by the L3 routing table search, adedicated VC table t3 is searched by the datalink layer-network layertranslation unit 203 to check if there is an entry for the destinationaddress in this dedicated VC table t3 (step S9). This dedicated VC tablet3 is managed by the datalink layer control unit 206 and an entry isregistered in this dedicated VC table t3 when L2 forward is made withoutmaking L3 forward at a router in a middle. By searching through thisdedicated VC table t3, it is possible to determine the connection ID tobe attached to the packet to be outputted from the destination L3address. Consequently, by using this dedicated VC table t3, it becomespossible to carry out the L2 transfer by routers at a next and fartherstages, so as to realize a high speed packet transfer. When acorresponding entry is found by the dedicated VC table search, theoperation proceeds to the step S12 described below.

When no corresponding entry is found by the dedicated VC table search, adefault VC table t2 is searched by the datalink layer-network layertranslation unit 203 (step S10). This default VC table t2 registers therouters/terminals existing in the same LAN, for a use in a case of theL3 packet transfer to a next hop, hop by hop. When a corresponding entryis found by the default VC table search, the operation proceeds to thestep S12 described below.

When no corresponding entry is found by the default VC table searcheither, the output connection ID remains unknown, so that the L2 addressis resolved from the L3 address by using ARP (Address ResolutionProtocol), a connection (VC) is set up, and a corresponding entry isregistered in the default VC table t2, while the packet is outputted byusing its output connection ID, at the datalink layer-network layertranslation unit 203 (step S11).

The packet with the output connection ID determined is then convertedfrom an L3 packet to an L2 frame at the datalink layer-network layertranslation unit 203 (step S12), and outputted to the LAN through thenetwork I/F unit 201 of the determined output I/F (step S13).

Also, when there is an entry from the upper layer (step S7), the stepsS8 to S13 described above is carried out similarly for the transmissionof a packet.

In the above described procedure, the dedicated VC table and the defaultVC table are provided separately, but it is also possible to combinethem to form a single table. It is further possible to form a singletable by combining the L3 routing table, the default VC table, and thededicated VC table, if desired. In this case, the L3 routing table has aformat as shown in FIG. 8, which differs from the L3 routing table t4shown in FIG. 7 in that the output connection ID (VPI/VCI) is registeredin a field for the output I/F as well, so that it suffices to searchthrough this table alone in determining the output connection ID, andtherefore the separate default VC table and dedicated VC table areunnecessary.

TRANSMISSION TERMINAL

The steps S7 to S13 in the above described flow chart of FIG. 7 for apacket transfer procedure at a router is a packet transmission procedurewhich is also applicable to a packet transmission at a terminal as well.

Here, another example of a transmission terminal for transmitting apacket will be described with references to FIG. 9 to FIG. 12.

The terminal (host) 602 in FIG. 1 for transmitting and receiving packetsin this embodiment can have an exemplary configuration as shown in FIG.9, which comprises: an ATM layer processing unit 621; an ATM cell-IPpacket conversion unit 622 connected with the ATM layer processing unit621; an IP layer processing unit 623 connected with the ATM cell-IPpacket conversion unit 622, and a VC management unit 624 and adestination management unit 627 connected with the IP layer processingunit 623. Here, the IP layer processing unit 623 includes a data packettransmission and reception unit 6231 for carrying out transmission andreception of data packets and a control message transmission andreception unit 6232 for carrying out transmission and reception ofcontrol messages, and the VC management unit 624 includes a VC controlunit 625 and a VC management table 626, while the destination managementunit 627 includes a destination control unit 628 and a destinationmanagement table 629.

Here, the VC management table 626 has an exemplary table content asshown in FIG. 10. This VC management table 626 stores a VC connectiontarget IP address, I/F, VPI/VCI, and status for each VC managed by theVC management unit 624. The status indicates whether each VC is alreadyin use somewhere or not.

Also, the destination management table 629 has an exemplary tablecontent as shown in FIG. 11. This destination management table 629stores a correspondence between a data transmission destination (whichcan be indicated by an IP address of a destination terminal, or by a netID of a destination network, for example), I/F, and VPI/VCI.

Next, a procedure for transmitting a data packet in this transmissionterminal of FIG. 9 will be described with reference to the flow chart ofFIG. 12.

When data to be transmitted (IP packet) is generated (step S161), thedestination management table 629 is referred to check if there exists anentry corresponding to the destination IP address in the generated IPpacket (S162). In a case where a corresponding entry exists at the stepS162, a corresponding I/F and a corresponding VPI/VCI are obtained fromthe destination management table 629 (step S163). Then, the ATM cell isassembled according to a prescribed format (step S168) and the datapacket, i.e., the assembled ATM cell, is transmitted (step S169).

In a case a where corresponding entry does not exist at the step S162, anext hop is determined by referring to an IP routing table providedwithin the IP layer processing unit 623 (step S164). Then, whether atransfer by a bypass pipe is wished or not is judged (step S165).

In a case where the transfer by a bypass pipe is not wished, the VCmanagement table 626 is referred to obtain I/F and VPI/VCI correspondingto the next hop (step S167). Then, the ATM cell is assembled accordingto a prescribed format (step S168) and the data packet, i.e., theassembled ATM cell, is transmitted (step S169).

In a case where the transfer by a bypass pipe is wished, the bypass pipeis created by using the control message and registered in thedestination management table 629 (step S166), and then, a correspondingI/F and a corresponding VPI/VCI are obtained from the destinationmanagement table 629 (step S163). Then, the ATM cell is assembledaccording to a prescribed format (step S168) and the data packet, i.e.,the assembled ATM cell, is transmitted (step S169).

BYPASS PIPE SET UP/RELEASE PROCEDURE (HARD STATE)

Now, a procedure for setting up or releasing a bypass pipe using a hardstate scheme in this embodiment will be described in detail. In a caseof ATM, the bypass pipe can be provided by either a PVC (PermanentVirtual Channel) or a VC within VP. The bypass pipe set up/releaseprocedure to be described below is equally applicable to either case, sothat only a case of using PVC will be described below as an illustrativeexample.

In an exemplary case in which a router-A commands set up/release of abypass pipe from a router-A to a router-D through a router-B, arouter-C, and ATM-LANs provided between routers as shown in a part (a)of FIG. 13, there are two possible outlines for a control messagesequence to be used at a time of set up as indicated in parts (b) and(c) of FIG. 13, and two possible outlines for a control message sequenceto be used at a time of release as indicated in parts (d) and (e) ofFIG. 13. In setting up or releasing the bypass pipe, it is preferable torewrite an ATM routing control table within one cell time in order tomaintain a transfer efficiency for data packets. In view of this fact, acase of using the control message sequences as outlined in a part (b)(set up-1) and a part (e) (release-2) of FIG. 13 will be described indetail first.

In this case, detailed control message sequences to be used at a time ofbypass pipe set up are shown in FIGS. 14, 15, and 16, where FIG. 14shows a control message sequence for a case in which the bypass pipe hasbeen set up to a target router, FIG. 15 shows a control message sequencefor a case in which the bypass pipe has been set up to an intermediaterouter, and FIG. 16 shows a control message sequence for a case in whichthe bypass pipe has not been set up.

As indicated in each of FIGS. 14, 15, and 16, a black dot symbol inthese figures represents a router which made a bypass pipe set uprequest command (router-A in this case), and a partially black squaresymbol in these figures represents a completion of an ATM transfer setup (ATM layer level set up). Also, a solid line with an arrow in thesefigures represents a control message. Here, a control message at a timeof bypass pipe set up is transferred to a neighboring router hop by hop,using a default VC provided for this purpose. In addition, a rectangularenclosure with an arrow in these figures represents a state transitioninside a router and an operation of a router at that time, where eachoperation is indicated in an abbreviated format of "AS(numeral)" whosecontent is specified in a table shown in FIG. 17.

In FIG. 17, each operation is specified in terms of the following parts.A "Transmission Packet" part indicates a type of packet to betransferred. "Bypass Pipe Management Table" parts (output side and inputside) indicate registration or deletion of a bypass pipe managementtable as shown in FIG. 18C for managing from which input port to whichoutput port the dedicated VCs are connected. In further detail, thebypass pipe management table of FIG. 18C has an entry for each bypasspipe ID which specifies VCID, VPI/VCI, and port at the input side andthe output side, along with its state (internal state). An "ATMTransfer" part indicates a set up or release of the L2 routing tablewithin the router to carry out the ATM transfer. An "IP-VCCorrespondence table/IP Routing table" part indicates registration ordeletion of an IP-VC correspondence table as shown in FIG. 18D and an IProuting table as shown in FIG. 18E. Here, the IP-VC correspondence tableof FIG. 18D is used in determining which VC should the packet beoutputted at a time of transferring the packet from the first router ofthe bypass pipe according to the destination IP address of the packet.This IP-VC correspondence table of FIG. 18D is set up in the router atan entrance of the bypass pipe when the bypass pipe is set up.

Also, each interface is provided with a VC management table as shown inFIG. 18A for specifying a VCID and a target IP address for each VPI/VCI,and an available VC table as shown in FIG. 18B for specifying a VCID foreach target IP address, in addition to the IP-VC correspondence table ofFIG. 18D.

On the other hand, each node is provided with the IP routing table ofFIG. 18E for specifying a next hop IP address, an interface, a virtualnext hop IP address, and a packet count for each destination IP address,in addition to the bypass pipe management table of FIG. 18C. Here, thenext hop IP address indicates an address of a next node in a case of ausual hop by hop transfer, and the virtual next hop IP address indicatesan address of a terminal point node of a bypass pipe which correspondsto a next hop in terms of IP and which is to be used in a case of atransfer by a bypass pipe, while the packet count indicates a number ofpackets transferred, which is to be used as a statistical information indetermining a timing for the bypass pipe set up.

Now, the detailed control message sequences of FIGS. 14, 15, and 16 willbe described in further detail one by one.

FIG. 14 is a control message sequence for a case in which the bypasspipe has been set up completely from the router-A to the router-D. Theblack dot symbol indicates that the router-A receives the bypass pipeset up request command. When this command is received, the router-Achanges the internal state for a pipe ID=#1 from an "idle" state to a"set up request transmission" state by changing a state of the pipeID=#1 in the bypass pipe management table. Then, the VCID and the portused at the output side are registered in the bypass pipe managementtable. In addition, the bypass pipe set up request message istransmitted to the router-B which is a next stage router on the way tothe router-D. This message includes the pipe ID, the VCID to be used,the final destination address, and the sender address. In this example,the pipe ID is #1, the VCID is #2, the final destination address is therouter-D, the sender address is the router-A. Here, the finaldestination address and the sender address are those contained in thebypass pipe set up request message, and not those contained in theheader of the IP packet. These series of operations are indicated by"AS1" in FIG. 17.

The router-B starts to operate when the bypass pipe set up requestmessage transmitted from the router-A is received. First, the router-Bchecks the condition P1: whether the dedicated VC to the router-A isavailable and whether the router-A is permitted to set up the bypasspipe to the router-B. Then, the router-B checks whether the router-Bitself is the last router of the bypass pipe or not by looking up thefinal destination address of the received message. Here, the conditionfor becoming the last router is given by the condition P2: a case ofeither "a link to a next router to which the bypass pipe set up requestmessage is to be sent is not ATM" or "it is in the identical sub-net asthe final destination address". For this condition P2, it is alsopossible to consider a case of "a link to a next router to which thebypass pipe set up request message is to be sent is not ATM" or "it isidentical to the final destination address".

In this example, the link to which the bypass pipe set up requestmessage is to be sent is ATM and the final destination address is therouter-D, so that the router-B is not the last router of the bypasspipe. Thus, the router-B changes the internal state for the pipe ID=#1from an "idle" state to a "set up request reception" state. Then, thebypass pipe set up request message is transmitted to the router-C whichis a next stage router on the way to the router-D. Here, the content ofthe bypass pipe set up request message has the same pipe ID and finaldestination address as those sent by the router-A, while the VCID ischanged to that used by the router-B. After this message is transmitted,the VCIDs and ports used here are registered in the input side and theoutput side of an entry for the pipe ID=#1 in the bypass pipe managementtable.

The router-C also checks whether the dedicated VC between the router-Band the router-C is available according to the condition P1, and whetherit is the last router of the bypass pipe according to the condition P2,just as in the router-B. In this example, it is recognized that it isnot the last router of the bypass pipe. Thereafter, the router-C carriesout the operations similar to those of the router-B described above, andtransmits the bypass pipe set up request message to the router-D.

When the bypass pipe set up request message is received from therouter-C, the router-D checks whether the dedicated VC between therouter-C and the router-D is available according to the condition P1,and whether it is the last router of the bypass pipe according to thecondition P2. In this example, the final destination of this bypass pipeset up request message is the router-D, it is recognized that it is thelast router of the bypass pipe. Then, the router-D changes the internalstate from an "idle" state to an "exit" state, and returns a bypass pipeset up response message to the router-C from which the bypass pipe setup request message has arrived. This message contains the pipe ID, theVCID, and the sender address. Here, the sender address is the router-D.Then, the VCID and port used here are registered in the input side ofthe bypass pipe management table.

When the bypass pipe set up response message is from the router-D, therouter-C changes the internal state from the "set up request reception"state to a "relay" state. Then, a previous stage router is recognizedfrom the VCID registered in the input side of the bypass pipe managementtable and the bypass pipe set up response message is transmitted to therouter-B. Here, the content of this message retains the pipe ID, thefinal destination address, and the sender address as received whilechanging the VCID to that registered in the bypass pipe managementtable. Then, the ATM routing table is changed accordingly so as toenable the ATM transfer.

When the bypass pipe set up response message is received from therouter-C, the router-B operates similarly as the router-C, and transmitsthe bypass pipe set up response message to the router-A.

When the bypass pipe set up response message is received from therouter-B, the router-A changes the internal state from the "set uprequest transmission" state to an "entrance" state, and registers theVCID and port used here in the input side of the bypass pipe managementtable. Also, the router-A changes the output target of the IP packetfrom the default VC to the currently set up bypass pipe by registeringthe IP address of the IP packet and the VPI/VCI of the bypass pipe intothe IP-VC correspondence table. In addition, the virtual next hop IPaddress for the IP routing table (L3 routing table) as shown in FIG. 18Eis registered. By this, the set up of the bypass pipe from the router-Ato the router-D is finished.

FIG. 15 is a control message sequence for a case in which the bypasspipe has been set up only to an intermediate point. The black dot symbolindicates that the router-A receives the bypass pipe set up requestcommand just as in a case of FIG. 14. Here, the operations from therouter-A to the router-C are the same as in a case of FIG. 14.

When the bypass pipe set up request message is received from therouter-C, the router-D checks whether the dedicated VC is availableaccording to the condition P1. Then, when the condition P1 is notsatisfied, the router-D leaves the internal state in the "idle" state,and returns the bypass pipe set up rejection message to the router-C.This message contains the final destination address, the sender address,the pipe ID, and the VCID. In this example, the final destinationaddress is the router-D, and the sender address is the router-A.

When the bypass pipe set up rejection message is received from therouter-D, the router-C changes the internal state from the "set uprequest reception" state to an "exit" state. Then, the bypass pipe setup response message is transmitted to the router-B. Here, the finaldestination address of this message is set to be the router-C. Therouter-C then finishes its operation by deleting the output side of thebypass pipe management table.

Hereafter, the router-B and the router-A operates similarly as in a caseof FIG. 14, such that eventually the bypass pipe from the router-A tothe router-C is set up.

FIG. 16 is a control message sequence for a case in which the bypasspipe has not been set up at all as the bypass pipe set up requesttransmitted from the router-A is rejected by the neighboring router-B.

In this case, when the bypass pipe set up request message is received,the router-B checks the condition P1 and recognizes that there is noavailable dedicated VC, so that the router-B returns the bypass pipe setup rejection.

When the bypass pipe set up rejection message from the router-B isreceived, the router-A changes the internal state from the "set uprequest transmission" state to the "idle" state, and deletes the outputside of the bypass pipe management table, such that eventually no bypasspipe is set up.

Next, detailed control message sequences to be used at a time of bypasspipe release are shown in FIGS. 19, 20, and 21, where FIG. 19 shows acontrol message sequence for a case in which the bypass pipe is releasedby a router at an entrance of the bypass pipe, and FIG. 20 shows acontrol message sequence for a case in which the bypass pipe is releasedby a router in a middle of the bypass pipe. In either case, the releaseis not a partial one and the bypass pipe is to be entirely released.FIG. 21 shows a control message sequence for an exemplary case of anexceptional processing in which the bypass pipe release request messagesare issued simultaneously from two routers.

As indicated in each of FIGS. 19, 20, and 21, a black dot symbol inthese figures represents a router which made a bypass pipe releaserequest command. Also, a solid line with an arrow in these figuresrepresents a control message. Here, a control message at a time ofbypass pipe release is also transferred to a neighboring router hop byhop, using a default VC provided between the neighboring routers, justas in a case of the bypass pipe set up request message. In addition, arectangular enclosure with an arrow in these figures represents a statetransition inside a router and an operation of a router at that time,where each operation is indicated in an abbreviated format of"AR(numeral)" whose content is also specified in the table shown in FIG.17 described above.

Now, the detailed control message sequences of FIGS. 19, 20, and 21 willbe described in further detail one by one.

FIG. 19 is a control message sequence for a case in which a router at anentrance of the bypass pipe issues the bypass pipe release requestcommand. The router-A which is the router at an entrance of the bypasspipe changes the internal state from the "entrance" state to a "releaserequest (downward) transmission" state, and deletes an entrycorresponding to this bypass pipe from the IP-VC correspondence tablesuch that the transmission packet does not use this bypass pipe. Then,the router-A transmits the bypass pipe release request (downward) to therouter-B. This message contains the pipe ID of the bypass pipe to bereleased, the VCID, and the sender address. In this case, the senderaddress is the router-A.

When the bypass pipe release request message is received from therouter-A, the router-B changes the internal state from the "relay" stateto a "release request (downward) transmission" state. Then, the router-Bdeletes the input side of the bypass pipe management table, andtransmits the bypass pipe release response (upward) to the router-Awhile transmitting the bypass pipe release request (downward) to therouter-C. Here, the bypass pipe release response message contains thepipe ID, the VCID, and the sender address. In this case, the senderaddress is the router-B. On the other hand, the sender address of thebypass pipe release request message is the router-A which originallyissued this message.

When the bypass pipe release request message is received from therouter-B, the router-C operates similarly as the router-B.

When the bypass pipe release request message is received from therouter-C, the router-D changes the internal state from the "exit" stateto the "idle" state. Then, the router-D deletes the input side of thebypass pipe management table and transmits the bypass pipe releaseresponse message to the router-C.

When the bypass pipe release response message is received, each of therouter-C, the router-B, and the router-A changes the internal state fromthe "release request (downward) transmission" state to the "idle" state.By means of these operations, the bypass pipe is released.

FIG. 20 is a control message sequence for a case in which a router in amiddle of the bypass pipe (assumed to be the router-B here) issues thebypass pipe release request command. When the bypass pipe releaserequest command is received, the router-B changes the internal statefrom the "relay" state to a "release request (upward, downward)transmission" state. Then, the router-B deletes the ATM routing table inorder to finish the ATM transfer, and transmits the bypass pipe releaserequest (upward) packet to the router-A while transmitting the bypasspipe release request (downward) message to the router-C.

The router-C and the router-D operate similarly as in a case of FIG. 19.

When the bypass pipe release request (upward) is received from therouter-B, the router-A changes the internal state from the "entrance"state to the "idle" state. Then, the router-A deletes the virtual nexthop IP address of the IP routing table by looking up the user in thebypass pipe management table in order to switch the IP packet transferfrom the bypass pipe to the default VC. Also, the router-A deletes theentry for this bypass pipe from the IP-VC correspondence table whiledeleting the output side of the bypass pipe management table. Then, therouter-A finishes its operation by transmitting the bypass pipe releaseresponse (downward) message to the router-B.

When the bypass pipe release response (downward) is received from therouter-A, the router-B changes the internal state from the "releaserequest (upward, downward) transmission" state to the "release request(upward) transmission" state. Then, the router-B finishes its operationby deleting the input side of the bypass pipe management table.

FIG. 21 is a control message sequence for an exemplary case of anexceptional processing at a time of the bypass pipe release, in whichthe bypass pipe release request messages are issued simultaneously fromthe router-A and the router-B. At a time of issuing the bypass piperelease request messages from the router-A and the router-B, theoperations are the same as in the normal cases described above.

When the bypass pipe release request message is received from therouter-A, the router-B changes the internal state from the "releaserequest (upward, downward) transmission" state to the "release request(downward) transmission" state, and deletes the input side of the bypasspipe management table.

On the other hand, when the bypass pipe release request message isreceived from the router-B, the router-A changes the internal state fromthe "release request (downward) transmission" state to the "idle" state,and deletes the output side of the bypass pipe management table.

The procedures and the internal operations for the bypass pipe set upand release described above can be summarized in terms of the statetransitions inside the router as shown in FIG. 22. It is to be notedthat, in the above description, the procedures and the internaloperations for the bypass pipe set up and release have been describedonly for a normal case in which the packet reaches without a failure.However, in practice, there is also a possibility for the packet to belost. For this reason, a timer is activated whenever the request messageis transmitted, such that when there is no response to that messagewithin a prescribed period of time (i.e., a case of time-out), a newoperation is to be carried as indicated in FIG. 22.

In FIG. 22, each node (enclosure) represents the internal state of therouter, and there are nine internal states altogether. The solid lineswith arrows among these internal states represent the state transitions.Each solid line with an arrow is accompanied by the indication of anevent causing that state transition and an operation at that time. Forinstance, when the bypass pipe set up command arrives in the "idle"state, the internal state is changed to the "idle & set up requesttransmission" state, and the operation AS1 is carried out. Also, in FIG.22, "|P1" and "|P2" indicate negations of the above described conditionsP1 and P2, i.e., cases in which the conditions P1 and P2 do not hold,respectively.

It is to be noted here that, although not depicted in this statetransition diagram of FIG. 22, in practice, when the router is in any ofthe "entrance" state, the "relay" state, and the "exit" state, whetherthe bypass pipe is connected is checked regularly, and it is necessaryto return to the "idle" state whenever the bypass pipe is not connected.

Next, with references to flow charts of FIGS. 23 and 24, an exemplarybypass pipe set up procedure using control message exchanges in anexemplary situation shown in FIG. 25 will be described.

In FIG. 25, ATM-LANs 11 to 15 (#1 to #5) are inter-networked by routers1A, 1B, and 1C having network layer processing units, where each networklayer processing unit corresponds to the network layer processing unit35 in a configuration of FIG. 5. In this example, there are a default VC10x with VCI=$x between the router 1A and the router 1B and a default VC10a with VCI=$a between the router 1B and the router 1C, and a bypasspipe formed by a dedicated VC 10y with VCI=$y and a dedicated VC 10bwith VCI=$b is to be set up from the router 1A to the router 1C.

First, when the bypass pipe set up request is recognized (step S2001),the router 1A looks up the internal routing table (step S2002) andtransmits the bypass pipe set up request message to a next stage router1B (step S2003) in order to set up the dedicated VC between this router1A and the next stage router 1B. Here, the bypass pipe set up requestmessage is to be transferred hop by hop between the neighboring routers,so that it is always transmitted through the default VC between theneighboring routers.

In this embodiment, the VP pipe is established between the neighboringrouters, and the default VC and the dedicated VC to be used for thedatagram transfer are both contained in this VP. In this case, thebypass pipe set up request message contains at least (1) the IP addressof the start point router, (2) the IP address of the end point router,and (3) the VCI value desired to be used within the VP pipe.

For example, in a case the router 1A desires to establish the bypasspipe, the router 1A captures the VCI value "$y" of the dedicated VCwithin the VP between this router 1A and the router 1B, and transmitsthe datagram via that dedicated VC (step S2004).

Here, the router 1A may start the transmission of the datagram towardthe router 1C through this VC with VCI=$y immediately, or at a certainperiod of time after the sending of the message, or after a messagereception acknowledgement is received from the router 1B side in someway. As will be described below, in any of these cases, this VC has thenetwork layer processing unit in a middle of the route as the receivingtarget, so that even if this VC is not connected with the end pointrouter end-to-end, it is possible to transmit the datagram through thisVC. At this point, VCI=$y is going to be registered as the destinationdatalink layer identifier (VPI/VCI value in this embodiment) of therouter 1C on the routing table within the router 1A. Here, however, themetric value remains unchanged and does not decrease even when thededicated VC is established.

The router-B receives the bypass pipe set up request message through thedefault VC between the router 1A and the router 1B as described above(step S2005). By means of this message, the router-B can recognize thefact that "it is requested to establish this VC with VCI=$y as thebypass pipe to the router 1C in the VP containing the default VC". Atthis point, the L2 routing table of the datalink layer switch unit 202within the router 1B may be set up such that the connection target ofthis VC with VCI=$y is set as the network layer processing unit withinthe router 1B, or the connection target may be as the network layerprocessing unit within the router 1B for all VCI values within the VP inadvance at a time of the VP establishment (step S2006). At this point,the VC with VCI=$y in this VP is connected to the network layerprocessing unit within the router 1B so that it is not ATM transfer, butit is possible even at this point to transmit the datagram through thisVC to reach the router 1C eventually.

Next, with regard to the end point router of the bypass pipe set uprequest message, the network layer processing unit of the router 1Bsearches the next hop router by looking up its own routing table (stepS2007). In a case this router 1B is the relay router (step S2008 NO),the router 1B selects the next hop router which is the router 1C bylooking up the routing table (step S2009). Then, the router 1B capturesa still unused VCI value ($b for example) in the VP between this router1B and the router 1C, and transmits the bypass pipe set up requestmessage through the default VC to the next hop router 1C by rewritingthe desired VCI value of the above (3) to $b (step S2010).

Here, at the router 1B, it is possible to generate the dedicated VC bydirectly connecting this VC and the VC with VCI=$y in the VP between therouter 1A and the router 1B at the ATM layer. Here, the directconnection at the ATM layer is realized by directly setting up theheader conversion table of the add/drop and header conversion unit 32 asdescribed above in a case the network layer processing unit whichreceived the bypass pipe set up request message itself is the two portrouter, or by directly setting up the the switch table in the switchinput/output processing unit as described above in a case the networklayer processing unit which received the bypass pipe set up requestmessage itself is the multi-port router, or by directly issuing theprimitive for the set up to the processing function governing the tableset up (step S2011). One of the feature of the present invention lies inthis point.

This table set up may be carried out immediately after the reception ofthe bypass pipe set up request message, or at a certain period of timeafter the message has been sent out to the next stage router, or after amessage reception acknowledgement is received from the next stage routerin some way.

FIG. 25 shows a situation (intermediate state) of the default VC and thededicated VC for the datagram transfer using the router 1A as the startpoint after the above described procedure has been carried out.

Up to now, the procedure for setting up or releasing a bypass pipe usinga hard state scheme has been described according to the control messagesequences as outlines in parts (b) and (e) of FIG. 13. Alternatively, itis also possible to carry out the set up or the release of a bypass pipeaccording to the control message sequences as outlined in parts (c) (setup-2) and (d) (release-1) of FIG. 13, where a part (c) of FIG. 13 showsa control message sequence for the set up which is similar to that of apart (e) of FIG. 13 for the release as described above, while a part (d)of FIG. 13 shows a control message sequence for the release which issimilar to that of a part (b) of FIG. 13 for the set up.

More specifically, the control message sequence as outlined in a part(c) of FIG. 13 is a case in which the bypass pipe is set up step by stepusing sequential exchange of the bypass pipe set up request message andthe bypass pipe set up response message between each neighboringrouters.

In this case, when the router-A requests the setup of the bypass pipe,the router-A transmits the bypass pipe set up request message to therouter-B. In response, if the set up of the requested bypass pipe is tobe permitted, the router-B transmits the bypass pipe set up responsemessage to the router-A. By means of this, the router-A can recognizethat the dedicated VC has been set up between the router-A and therouter-B, so that the router-A makes the setting to transmit the datapackets through this newly set up dedicated VC. At this point, thededicated VC has not been set up beyond the router-B yet, so that therouter-B carries out the conventional network layer transfer to therouter-C.

Next, the router-B determines whether to set up the bypass pipe betweenthis router-B and the next stage router-C as well, and in a case ofsetting up such a bypass pipe. the router-B transmits the bypass pipeset up request message to the router-C. Then, when the bypass pipe setup response message from the router-C is received, the router-B makesthe setting to carry out the datalink layer transfer within thisrouter-B between the dedicated VC for the packet transfer from therouter-A to the router-B and the dedicated VC for the packet transferfrom the router-B to the router-C. By means of this, the bypass pipe hasbeen set up from the router-A to the router-C, and the transfer at therouter-B can be switched from the conventional network layer transfer tothe faster datalink layer transfer.

Here, whether or not to transmit the bypass pipe set up request messageto a next stage router can be determined by manners similar to those fordetermining a timing for bypass pipe set up/release which will bedescribed in detail below.

By repeating the similar operation at the router-C as well, it ispossible to set up the bypass pipe from the router-A to the router-D.

BYPASS PIPE SET UP/RELEASE PROCEDURE (SOFT STATE)

Next, a procedure for setting up or releasing a bypass pipe using a softstate scheme in this embodiment will be described in detail.

In short, this scheme operates as follows. In this scheme, thetransmitting side router can transmit the bypass pipe set up requestmessage regularly at a certain time interval. Then, the router at anintermediate stage of the bypass pipe is given a time-out value for thebypass pipe, such that this time-out value is reset by the reception ofthe bypass pipe set up request message, for example. By means of this,it is possible to prevent the bypass pipe that is no longer used frombeing left as a garbage. Alternatively, the router at an intermediatestage of the bypass pipe can monitor a presence or absence of the celltraffic in each bypass pipe, and when there is no traffic in some bypasspipe over a certain period of time, it judges that this bypass pipe isno longer used and resets this bypass pipe, i.e., changes the receptiontarget of the VC constituting that bypass pipe to the router processingunit within this router and resets the information concerning thetransmission source and the reception target for that VC. In thismanner, the similar effect as described above can also be achieved.

Here, it is not necessary for the bypass pipe set up request message tocarry a set up request for just one bypass pipe per one message, and itis possible for a single message to carry set up requests for aplurality of bypass pipes. In general, a number of bypass pipes cantrace the identical route in a course of reaching to their respectiveend point routers, so that it is useful to carry set up requests for aplurality of dedicated VCs in the bypass pipe set up request messagefrom viewpoints of the reduction of the traffic and the ease of themanagement. In particular, in a case of requesting the set up of aplurality of bypass pipes at once as in a case of the abnormality to bedescribed below, this scheme is also useful in preventing the occurrenceof the congestion at the CPU within the router and the network.

Now, the bypass pipe set up/release procedures in this scheme will bedescribed in detail.

In an exemplary case in which a router-A commands set up/release of abypass pipe from a router-A to a router-D through a router-B, arouter-C, and ATM-LANs provided between routers as shown in a part (a)of FIG. 26, there are two possible outlines for a control messagesequence to be used at a time of set up as indicated in parts (b) and(c) of FIG. 26, and two possible outlines for a control message sequenceto be used at a time of release as indicated in parts (d) and (e) ofFIG. 26.

Here, a case of using the control message sequence as outlined in a part(b) (set up-1) of FIG. 26 which is the receiver initiative soft statetype bypass pipe control protocol will be described in detail first. Inthis case, the bypass pipe management table of FIG. 18C described aboveshould be modified to include an additional "previous router" field forregistering an IP address of a previous stage router, which is to beregistered at a time of receiving the path message, and to be utilizedin determining a path of the bypass pipe.

In this case, the router-A regularly transmits a path message toward therouter-D in order to permit the bypass pipe up to the router-D andnotify the path of the bypass pipe to the intermediate routers. Each ofthe router-B and the router-C which are the intermediate routers in thisexample transfers this message to its next stage router, whileregistering the IP address of its previous stage router into theprevious router field of the bypass pipe management table in order torecord the path. Thus, the router-B registers the IP address of therouter-A, and the router-C registers the IP address of the router-B,while the router-D which received the path message registers the IPaddress of the router-C into the previous stage router field of thebypass pipe management table.

When the router-D wishes to utilize the bypass pipe, the router-Dtransmits a reservation message to the address registered in theprevious stage router field of the bypass pipe management table, whichis the router-C in this example. IN the bypass pipe management table,the dedicated VC to be used as the bypass pipe is registered in theinput side. This reservation message is transmitted regularly, and atimer T1 (not shown) is activated whenever this reservation message istransmitted, such that the same message is transmitted again when thistimer indicates the time-out.

When the reservation message is received from the router-D, the router-Cchecks the condition P3: this router is not the first router of thebypass pipe. When this condition P3 is checked, the router-C transmitsthe reservation message to the previous stage router-B, while rewritesthe ATM routing table to enable the ATM transfer between the dedicatedVC from the router-B to the router-C and the dedicated VC from therouter-C to the router-D. In addition, the router-C registers thededicated VCs into the input side and the output side of the bypass pipemanagement table, and activates a timer T2 (now shown) in order tomonitor, the fact that the reservation message is regularly transmitted.

The router-B operates similarly as the router-C, and transfers thereservation message to the router-A. When the reservation message isreceived from the router-B, the router-A recognizes that it is the firstrouter of the bypass pipe by checking the condition P3, and registersthe dedicated VC to the output side of the bypass pipe management table,while changing the IP routing table and the IP-VC correspondence table.Then, the router-A activates the timer T2 in order to monitor the factthat the reservation message is regularly transmitted. By means of theseoperations, the bypass pipe from the router-A to the router-D can be setup.

A case of using the control message sequence as outlined in a part (c)(set up-2) of FIG. 26 which is the sender initiative soft state typebypass pipe control protocol can also be realized similarly as in a caseof the receiver initiative soft state type bypass pipe control protocoldescribed above.

As for the bypass pipe release procedure in this scheme, there are twomethods including a method for sending an explicit release message, anda method for releasing the bypass pipe when the timer indicates thetime-out as the regularly transmitted reservation messages stoparriving. The control message sequences as outlined in a part (d)(release-1) and a part (e) (release-2) of FIG. 26 belong to the formermethod of sending an explicit release message.

In a case of a part (d) of FIG. 26 for releasing from the router-A side,the router-A changes the internal state from the "entrance" state to the"idle" state. Then, the router-A deletes the output side of the bypasspipe management table as well as the virtual next stage router from theIP-VC correspondence table and the IP routing table, and stops the timerT2. Then, the router-A notifies the release explicitly to the router-Bby sending the release message.

When the release message is received from the router-A, the router-Bchanges the internal state from the "relay" state to the "idle" state.Then, the router-B deletes the dedicated VC related to the bypass pipeto be released from the input side and the output side of the bypasspipe management table, rewrites the ATM routing table in order to stopthe ATM transfer, and stops the timer T2. Then, the router-B sends therelease message to the next router-C.

The router-C operates similarly as the router-B, and sends the releasemessage to the router-D.

When the release message is received from the router-C, the router-Dchanges the internal state from the "exit" state to the "idle" state.Then, the router-D deletes the input side of the bypass pipe managementtable, and stops the timer T1.

A case of a part (e) of FIG. 26 for releasing from the router-D side canalso be realized similarly as in a case of a part (d) of FIG. 26described above.

In this case, the router-D changes the internal state from the "exit"state to the "idle" state, and sends the release message to therouter-C. Then, the router-D deletes the input side of the bypass pipemanagement table, and stops the timer T1.

When the release message is received from the router-D, the router-Cchanges the internal state from the "relay" state to the "idle" state,deletes the input side and the output side of the bypass pipe managementtable, and rewrites the ATM routing table. Then, the router-C sends therelease message to the router-B, and stops the timer T2.

The router-B operates similarly as the router-C, and sends the releasemessage to the router-A.

When the release message is received from the router-B, the router-Achanges the internal state from the "entrance" state to the "idle"state. Then, the router-A deletes the output side of the bypass pipemanagement table as well as the virtual next stage router from the IP-VCcorrespondence table and the IP routing table, and stops the timer T2.

In the above, a case of explicit release has been described, but thereis also a case in which the release message packet is lost in a middle,so that it is necessary to make it possible to release the bypass pipeby using a local timer. Namely, the reservation message is to beregularly transmitted from the exit router while the bypass pipe isactive, so that when it is recognized that the reservation message hasstopped arriving, the bypass pipe can be released.

To this end, each router has the timer T2, which is reset whenever thereservation message arrives. When the reservation message has stoppedarriving and this timer T2 indicates the time-out, the router changesthe internal state to the "idle" state, and deletes the bypass pipemanagement table along with the ATM routing table, the IP routing table,and the IP-VC correspondence table relates to this bypass pipe.

The procedures and the internal operations for the receiver initiativesoft state type bypass pipe set up and release described above can besummarized in terms of the state transitions inside the router as shownin FIG. 27.

In FIG. 27, each node (circular enclosure) represents the internal stateof the router, and there are four internal states altogether. The solidlines with arrows among these internal states represent the statetransitions. Each solid line with an arrow is accompanied by theindication of an event causing that state transition and an operation atthat time. Here, each operation is indicated in an abbreviated format of"A(numeral)" whose content is specified in a table shown in FIG. 28similar to the table of FIG. 17 described above.

Similarly, the procedures and the internal operations for the senderinitiative soft state type bypass pipe set up and release describedabove can be summarized in terms of the state transitions inside therouter as shown in FIG. 29 similar to the state transition diagram ofFIG. 27. Here, each operation is indicated in an abbreviated format of"B(numeral)" whose content is specified in a table shown in FIG. 30similar to the table of FIG. 17 described above.

Next, with reference to the flow chart of FIG. 31, the operation of therouter in a case of a change in the routing table of the router due tothe routing protocol operation will be described. Here, the change ofthe routing table includes a case corresponding to a change of thetopology of the internet environment, a case corresponding to a changeof the metric value that can happen in a case of an abnormality such asthe breakdown of an intermediate router or ATM-LAN, etc.

In the following, a case in which the bypass pipe route is changed willbe described. In this case, the change of the routing table is handledas follows.

For the neighboring router, when the router processing unit of therouter recognizes an occurrence of an abnormality such as a case inwhich the routing information that is supposed to be transmittedregularly fails to arrive, or a case in which a calculation result ofthe metric value has increased (step S4002), this router processing unitrewrites the L2 routing table for the dedicated VC connected toward thatneighboring router, to make this router processing unit itself as thereception target of that VC (step S4004). Consequently, as for thedatagram received from that VC which had been the dedicated VC untilthen, the transfer is continued according to this updated routing tablein that router processing unit.

Here, if this dedicated VC becomes out of use as the outing informationaccording to the existing routing protocol such as RIP is transmittedtoward the upstream side of this dedicated VC, and the routing route haschanged subsequent to the recognition of the abnormality on the upstreamside, the registered information on this dedicated VC will be eventuallydeleted within a certain period of time by the time-out, etc. caused asthe bypass pipe set up request message that is supposed to betransmitted regularly fails to arrive, or as the traffic stops existingin that VC.

On the other hand, when the "entrance" state router recognized thechange of the routing table (step S4002 YES and step S4007 YES), thebypass pipe set up request message is issued according to the newlyrewritten routing table in this router. Thereafter, the bypass pipe setup procedure is carried out again according to the procedure of FIGS. 23and 24 described above, for example (step S4008). Then, the datagram canbe transmitted through this newly set up bypass pipe.

At a time of the breakdown of the network or the router at anintermediate stage, the changes can occur in a plurality of routingtables at once, so that the bypass pipe setup request message to benewly issued makes a plurality of set up requests for the bypass pipesin an identical direction simultaneously within this message. By meansof this, it is possible to reduce a number of bypass pipe set up requestmessage packets within the network, while the processing function (suchas CPU) within the router for handling this message can handle theserequests within this single message, so that it is also possible toreduce a processing load and achieve a quick recovery.

It is to be noted that a case of explicitly sending the bypass pipe setup request message has been described above, but it is also possible forthe start point router to immediately start transmitting the datagramthrough an unused VC of the new route. In this case, the algorithm ofFIGS. 40 and 41 to be described below is going to be employed.

BYPASS PIPE SET UP PROCEDURE (IN-BAND)

Next, a procedure for setting up or releasing a bypass pipe using anin-band scheme for handling the control messages will be described indetail. In this scheme, the control packet for commanding the bypasspipe set up/release os transferred through the dedicated VC to be usedas a constituent element of that bypass pipe itself, that is, the datapacket and the control packet are transferred by the identical dedicatedVC.

FIG. 32 shows a control message sequence for the bypass pipe set up inthis scheme, for an exemplary case of setting up the bypass pipe fromthe router R2 to the router R4 through the router R3 and the ATM-LANsbetween the routers as indicated in a part (a) of FIG. 32. In this case,as indicated in a part (b) of FIG. 32, at a time of the bypass pipe setup, the router R2 for commanding the set up of the bypass pipe from therouter R2 to the router R4 transmits the "Bypass Pipe Setup" message tothe router R3 through the dedicated VC-A. When this "Bypass Pipe Setup"message is received from the router R2, the router R3 transmits the"Bypass Pipe Setup" message to the router R4 through the dedicated VC-B.In response, the router R4 transmits the "Bypass Pipe Ack" message tothe router R3 through the dedicated VC-B, and then the router R3transmits the "Bypass Pipe Ack" message to the router R2 through thededicated VC-B. By means of these operation, the bypass pipe from therouter R2 to the router R4 as indicated in a part (c) of FIG. 32 isestablished.

As for the bypass pipe release, the cell flow is monitored at eachrouter, and the bypass pipe is released by the judgement of each routerusing appropriate timer in this scheme.

CASE OF USING SVC

Up to this point, it has been assumed that the VC is given in a form ofa PVC. However, it is also possible for the VC to be given in a form ofan SVC (Switched Virtual Channel).

In a case of using the SVC, the bypass pipe set up procedure can berealized in any of the following four methods.

(1) After the ATM signaling is completed, the control messages aretransmitted in the same direction by the same procedure as in a case ofusing the PVC described above.

(2) After the control messages are transmitted, the ATM signaling iscarried out in an opposite direction.

(3) After the ATM signaling is completed, the control messages aretransmitted in an opposite direction.

(4) The bypass pipe set up message is embedded into the ATM signalingmessage.

The method (1) is a method which uses the SVC but the SVC is handledsimilarly as the PVC by setting up the VC in advance.

It is noted here that it has been assumed in the above description thatthe default VC and some dedicated VCs are set up for the bypass pipecontrol in advance, but it is also possible to provide a VP of aprescribed capacity between the routers in advance instead. In such acase, the operations since the VC is established in the VP until the VCis released are the same as a communication scheme utilizing the VC.

In addition, instead of providing the VPs in mesh shape among all therouters in advance, it is also possible to utilize an SVP (Switched VP)in which the VP is connected between the routers by the ATM signalingupon an arrival of the data packet to be communicated (which makes thefirst VC request between these routers). In this case, the operationssince the VP is connected by the ATM signaling until the VP isdisconnected is the same as a communication scheme utilizing the VP.

The method (2) is a method which establishes the bypass pipe by usingthe bypass pipe set up request message. Here, the algorithm is similarto that shown in FIGS. 23 and 24 described above.

In this case, the first stage router generates the bypass pipe set uprequest message. Then, this message is forwarded to the next stagerouter by using the default VC according to the routing table providedin the router (steps S2001 to S2004 of FIG. 23).

When this message is received, the router of an intermediate stageestablishes the link layer connection (ATM connection in thisembodiment) between this router and the previous stage router, whileforwarding that message to the next stage router (Steps S2005 to S2010).In addition, the VC established between this router and the previousstage router is connected at the ATM layer with the VC established (bythe next stage router) between this router and the next stage router bythe setting of the L2 routing table (step S2011 of FIG. 24).

The last stage router establishes the link layer connection between thisrouter and the previous stage router, and sets the router processingunit within this router as the terminal point of that connection (stepS2006).

By means of a series of these operations, the bypass pipe can be set upin this method (2). In short, this is a method in which theestablishment of the bypass pipe is sequentially requested to the nextstage router explicitly by means of the bypass pipe set up requestmessage.

The method (3) is a method in which the establishment of the datalinklayer connection is carried out by the previous stage router, ratherthan the next stage router as in the method (2) described above. Morespecifically, this method can be carried out according to the flowcharts of FIGS. 33 and 34 as follows.

When the bypass pipe set up request is recognized, the datalink layerswitch unit of the first stage router-A which wishes to establish thebypass pipe recognizes the next stage router by looking up the routingtable within that router, and requests the establishment of thebidirectional VC between this router and the next stage router to theATM-LAN (steps S7001 to S7003). Here, the requested VC is abidirectional VC because the InARP message to be described below will betransmitted in an opposite direction in which case. At this point, aspecial message such as the bypass pipe set up request message is notissued.

Then, the intermediate stage router-B receives the bypass pipe set uprequest from the ATM-LAN in which the sub-net is shared with theprevious stage router-A (step S7006). Here, at this point, the use ofthis VC is unknown and the end point IP address to be the start point ofthis VC is also unknown, so that the router-B generates the InARPrequest message and transmits this InARP request message to this VC(step S7007).

Then, when the InARP request message reaches to the router-A, therouter-A returns its own IP address as the InARP response message, alongwith a destination sub-net ID of that VC indicating that it wishes touse this link layer connection (VC) as the dedicated VC between thisrouter and a particular sub-net identified by that sub-net ID either asa part of the InARP response message or as a separate message from theInARP response message, through that VC (step S7004). In the formercase, it is necessary to adopt a special format for the InARP responsemessage.

When this InARP response message is received, the router-B recognizesthat VC as the dedicated VC for the packets destined to that particularsub-net (step S7008). In addition, by looking up the routing tablewithin that router, the router-B requests the establishment of the VC tothe ATM-LAN connected with the next stage router-C (step S7011). Also,when that VC is established and it is recognized by the next stagerouter that this VC is for the bypass pipe, the VC of the previous stageand this VC are directly connected at the ATM layer by the setting ofthe L2 routing table within that router, such that these VCs can bepassed through by only the ATM layer processing (step S7012).

The final stage router-C recognizes that the VC requested to be set upto it is that for the bypass pipe with this router as the end point(S7008) according to the InARP response message (or a message followingthe InARP message) by carrying out the above described stepsS7006-S7008, and as this router is an "exit" router (step S7009 YES),this router connects that VC to the network layer processing unit withinthis router (step S7010).

In this case, it should be noted that an ID of the sub-net to be theterminal point of the bypass pipe is entered into the InARP responsemessage (or a separate message).

By means of a series of these operations, the bypass pipe can be set upin this method (3).

It is to be noted that this method (3) uses the bidirectional VC, sothat the dedicated VC given in a form of the bidirectional VC is goingto be produced. Hence, in order to prevent a plurality of suchbidirectional dedicated VC to be set up between any two routers, whenone bypass pipe set up procedure is carried out in one direction whileanother bypass pipe set up procedure is also carried out in an oppositedirection simultaneously such that the dedicated VC to the targetsub-net has already been established in that one direction by theprocedure in the opposite direction at some intermediate stage router,this intermediate stage router may directly connect these VCs at the ATMlayer by the setting of the L2 routing table, so as to reduce timerequired for the bypass pipe set up considerably and simplify the bypasspipe set up procedure.

The method (4) is a method which carries out the bypass pipe set up byutilizing the ATM signaling. Here, for the ATM signaling, the so calledwell known VC for the ATM signaling is utilized.

In FIG. 35, several control message sequences for the bypass pipe set upand release in this method are shown for an exemplary case of setting upor releasing the bypass pipe as indicated in a part (e) of FIG. 35 fromthe router R2 to the router R4 through the router R3 and the ATM-LANsprovided between the routers as indicated in a part (a) of FIG. 35.Here, each ATM-LAN has a call control device 605 for handling the ATMsignaling therein.

As the control message sequence for the bypass pipe set up, threesequences are shown in parts (b), (c), and (d) of FIG. 35.

In the set up-1 shown in a part (b) of FIG. 35, the SETUP message of theATM signaling is sequentially transmitted through the call controldevices 605, from the router R2 to the router R3 first, and then fromthe router R3 to the router R4. After that, the CONNECT message of theATM signaling is sequentially transmitted through the call controldevices 605, from the router R4 to the router R3 first, and then fromthe router R3 to the router R2. When the CONNECT message is returned tothe router R2, the bypass pipe set up is completed.

In the set up-2 shown in a part (c) of FIG. 35, the SETUP message of theATM signaling is transmitted through the call control device 605-1 fromthe router R2 to the router R3. When the SETUP message is received fromthe router R2, the router R3 transmits the SETUP message through thecall control device 605-2 to the router R4 while at the same time therouter R3 also transmits the CONNECT message through the call controldevice 605-1 to the router R2. When the SETUP message is received fromthe router R3, the router R4 transmits the CONNECT message to the routerR3. When these CONNECT messages reached to the router R2 and the routerR3, respectively, the bypass pipe set up is completed.

In the set up-3 shown in a part (d) of FIG. 35, after the controlmessage sequence similar to the set up-2 described above is carried out,the router R4 transmits the Bypass Pipe Ack message which is anindependent control message different from those of the ATM signaling.When this Bypass Pipe Ack message is received at the router R2, thebypass pipe set up is completed.

On the other hand, as the control message sequence for the bypass piperelease, two sequences are shown in parts (f) and (g) of FIG. 35.

The release-1 shown in a part (f) of FIG. 35 is similar to the set up-1described above in that the REL (release) message of the ATM signalingis sequentially transmitted through the call control devices 605, fromthe router R2 to the router R3 first, and then from the router R3 to therouter R4. After that, the RELCOM (release complete) message of the ATMsignaling is sequentially transmitted through the call control devices605, from the router R4 to the router R3 first, and then from the routerR3 to the router R2. When the RELCOM message is returned to the routerR2, the bypass pipe i s released.

The release-2 shown in a part (g) of FIG. 35 is similar to the set up-2described above in that the REL message of the ATM signaling istransmitted through the call control device 605-1 from the router R2 tothe router R3. When the REL message is received from the router R2, therouter R3 transmits the REL message through the call control device605-2 to the router R4 while at the same time the router R3 alsotransmits the RELCOM message through the call control device 605-1 tothe router R2. When the REL message is received from the router R3, therouter R4 transmits the RELCOM message t o the router R3. When theseRELCOM messages reached to the router R2 and the router R3,respectively, the bypass pipe is released.

It is to be noted that the bypass pipe set up and the bypass piperelease are totally independent operations so that any desiredcombination of the above described control message sequences for the setup and the control message sequences for the release may be adopted.

TIMING FOR SWITCHING TO BYPASS PIPE

As for the timing for switching the data packet transfer from the usualIP transfer to the ATM level transfer using the bypass pipe, thefollowing two cases can be considered.

(i) The data packet transfer is switched to that using the bypass pipeafter the bypass pipe is set up all the way to the target node.

(ii) The data packet transfer is switched to that using the bypass pipefor any part of the bypass pipe that ha s been established by then, asthe bypass pipe is sequentially set up between each neighboring nodes.

As for the handling of the data packets before the data packets can betransmitted through the bypass pipe, the following two cases can beconsidered.

(i) The data packets are transferred by using the default VC before thebypass pipe set up is completed.

(ii) the data packets are kept awaiting at an entrance of the bypasspipe until it becomes possible to transfer the data packets through thebypass pipe.

In a case of using the connection-less network layer protocol as in thecurrent IP, either one of the above (i) or (ii) for the data packettransfer switching timing can be used, while it seems preferable totransfer the data packets by using the default VC before the bypass pipeset is completed.

In a case of the connection oriented network layer protocol, however, itseems preferable to transfer the data packets by using the bypass pipeafter the bypass pipe set up is completed up to the target node as faras the data packet transfer switching timing is concerned, while itseems appropriate to keep the data packets awaiting at an entrance ofthe bypass pipe until it becomes possible to transfer the data packetsthrough the bypass pipe as far as the data packet handling before thedata packet can be transmitted through the bypass pipe. Here, however,it is assumed that the connection set up request at the network layerlevel is to be encapsulated within the control message for the bypasspipe set up.

TIMING FOR BYPASS PIPE SET UP/RELEASE

Here, the timing for starting the above described bypass pipe setup/release procedure in this embodiment will be explained.

Each node can recognize a need to set up the bypass pipe and transmitthe control message in the following situations.

(1) When a statistical value calculated at that node has reached to aprescribed value.

(2) When any of the following messages is received:

(i) RSVP message (Path message, Reservation message, etc.);

(ii) ST II message (Connect message, Accept message, etc.);

(iii) TCP syn or fin message.

(3) When there is an instruction from the application (such as aninstruction which requests a securing of a bandwidth or a QoS by an IPlayer or an upper layer of the host, for example).

(4) When it is recognized that the bypass pipe has not been set up at atime of packet transmission.

Also, each node can recognize a need to release the bypass pipe in thefollowing situations.

(1) When a statistical value calculated at that node has reached to aprescribed value.

(2) When there is an instruction from the application (such as aninstruction which requests a securing of a bandwidth or a QoS by an IPlayer or an upper layer of the host, for example).

Here, it is to be noted that, in a case of dealing with the hard statetype protocol as in a case of the ST II, the bypass pipe is releasedonly by the explicit release request, whereas in a case of dealing withthe soft state type protocol as in a case of the RSVP (ResourceReservation Protocol), in addition to the release of the bypass pipe ata time of receiving the explicit release request, the bypass pipe canalso be released by each router on the route individually when eachrouter stops receiving the regularly transmitted bandwidth maintainingrequest (Refresh message in the RSVP).

Now, with reference to an exemplary configuration shown in FIG. 36,various types of nodes which can utilize the bypass pipe in thisembodiment will be explained. Here, for an exemplary case oftransmitting the data packet through the bypass pipe from left to rightin the figure, the following nodes may have a need to set up the bypasspipe between the router R2 and the router R4.

(1) A non-ATM transmission side host or application (such as the hostH1).

(2) An ATM transmission side host or application (such as the host H3).

(3) An initial stage cell switching router (such as the router R2).

(4) An intermediate stage cell switching router (such as the router R3).

(5) A final stage cell switching router (such as the router R4).

(6) An ATM reception side host or application (such as the host H4).

(7) A non-ATM reception side host or application (such as the host H2).

Among them, (1) can be realized in the ST II for example, while (7) canbe realized in the RSVP for example. The others can be realized by meansof the bypass pipe control messages.

Now, some exemplary cases of the timing for starting the bypass pipe setup procedure will be described in detail.

(A) Case of using statistical information

First, a case of using the statistical information in determining thetiming for starting the bypass pipe set up procedure will be described.This function can be realized by the datalink layer connection set upjudgement unit 205 in the configuration of FIG. 4 described above.

This datalink layer connection set up judgement unit 205 commands theset up or release of the datalink layer connection according to thestatistical information obtained by the network layer switch unit 204,and updates the datalink layer routing table in the datalink layerswitch unit 202 to reflect that statistical information. Here, when morepackets than a prescribed number are received, transmitted, ortransferred, the datalink layer connection is set up and this connectionis registered in the datalink layer routing table. Also, when no packetarrives over a prescribed period of time, the datalink layer connectionis released, and this connection is deleted from the datalink layerrouting table.

More specifically, this operation is carried out according to the flowchart of FIG. 37 as follows.

In this case of FIG. 37, there is provided a network layer packetstatistical information t5 which indicates a number of received packetsas a count value to be updated whenever the packet is transferred at thenetwork layer switch unit 204. The datalink layer connection set upjudgement unit 205 looks up this network layer packet statisticalinformation (step S31), and if the count value (COUNT) is greater than aconstant value (CONST1) (step S32 YES), the datalink layer connection(L2 connection) is set up (step S33), and an entry for this connectionis registered in the datalink layer routing table (L2 routing table)(step S34). Also, if the count value (COUNT) is less than anotherconstant value (CONST2) (step S35 YES), the datalink layer connection(L2 connection) is released (step S36), and an entry for this connectionis deleted from the datalink layer routing table (L2 routing table)(step S37). Then, the network layer packet statistical information t5 isreset (step S38), and after a wait for a prescribed timer time set by atimer (not shown) (step S39), the above operation is repeated.

Here, by setting CONST1=1 for example, it is possible to carry out thepacket transfer for the first packet alone, and then switch to the celltransfer for the subsequent packets.

Also, as a method for releasing the datalink layer connection, it ispossible to adopt a method in which a certain time value (CONST3) is setas the count value (COUNT) in the network layer packet statisticalinformation t5 whenever a packet is received, and sequentially reducedas time elapses, such that the datalink layer connection is releasedwhen the count value becomes 0.

Also, instead of using the network layer packet statistical informationas described above, it is also possible to use the statisticalinformation for the datalink layer data in a similar manner to releasethe datalink layer connection.

(B) Case of set up at a time of router activation

Next, a case of starting the bypass pipe set up procedure when aconnection target router is activated will be described. In this case,the operation is carried out according to the flow chart of FIG. 38 asfollows.

When the routing information is transmitted from the neighboring router(step S1001), the router can recognize that a new router has appeared atseveral hops ahead, and that this new router has not been connected tothe same ATM-LAN as this router according to its metric value.

Then, this router checks whether the default VC between this router andthe neighboring router has been established (step S1002), and if not,this router establishes the default VC for the datagram transfer betweenthis router and the neighboring router (step S1003). Then, this routercarries out a mutual confirmation using the user-user data, or a mutualconfirmation using the signaling data element, or a mutual confirmationusing InARP, with respect to the neighboring router (step S1004).Meanwhile, the routing information transmitted from the neighboringrouter is registered into the routing table in this router (step S1005).

Then, this router produces a correspondence table for the layer 3address and the layer 2 address/VPI/VCI (step S1006). Thiscorrespondence table corresponds to a table of FIG. 8 described above ortables of FIGS. 18D and 18E described above.

At this point, when this router recognizes that there exists a sub-netwhich is not connected by the direct end-to-end ATM connection atseveral hops ahead, this router checks if it is possible to establishthe bypass pipe (step S1007), and if so, the bypass pipe set upprocedure as described above is carried out (step S1008) to establishthe direct end-to-end ATM connection between this router and that newrouter, and then the datagram transmission by using that bypass pipe iscarried out (step S1009).

(C) Case of set up at a time of packet transmission

Next, a case of starting the bypass pipe set up procedure at a time ofthe packet transmission will be described. In this case, the operationis carried out according to the flow chart of FIG. 39, where the stepsidentical to those in the flow chart of FIG. 7 described above are giventhe same reference numerals in the figure and their descriptions will beomitted.

The operation according to FIG. 39 differs from that of FIG. 7 in that,after the dedicated VC search at the step S9 has failed, before thedefault VC search at the step S10 is carried out, whether or not to setup the dedicated VC is judged (step S21). Then, if the dedicated VC isto be set up, the dedicated VC setup procedure is carried out (step S22)and the operation proceeds to the step S12, whereas otherwise thedefault VC search at the step S10 is carried out.

(D) Case of set up at a time of resource reservation protocol reception

Next, a case of starting the bypass pipe set up procedure when aresource reservation protocol (such as RSVP, ST II, etc.) for thenetwork layer is received will be described.

In this case, the bypass pipe set up procedure is carried out when theset up message of the resource reservation protocol is received, and thebypass pipe release procedure is carried out when the release message ofthe resource reservation protocol is received. Here, in a case theresource reservation protocol is the RSVP, the session ID of the RSVPmay be used as the bypass pipe ID.

It is noted here that it is also possible to set up or release thebypass pipe according to the set up or release command of the transportlayer protocol such as TCP, instead of the resource reservationprotocol. In general, it is possible to set up or release the bypasspipe according to the connection set up or release message at the layerabove the network layer.

BYPASS PIPE SET UP/RELEASE PROCEDURE USING NO CONTROL MESSAGE

Next, the bypass pipe set up/release procedures without using anycontrol message in this embodiment will be described in detail.

First, with references to the flow charts of FIGS. 40 and 41, the firstbypass pipe set up/release procedure using no control message will bedescribed.

When the first stage router receives the datagram destined to thesub-net which is several hops ahead, to which the bypass pipe has notbeen set up and for which the direct delivery is not supported by thisrouter (step S3001), in order to establish the bypass pipe up to thatsub-net, this router looks up the routing table in this router to checkthe next stage router (step S3002), and captures one arbitrary unused VCto the next stage router other than the default VC within the VPconnected to the next stage router (step S3003). Then, the datagramdestined to that sub-net is transmitted through that VC (step S3004).

At the subsequent stage router, the terminal point of each unused VCbetween this router and the neighboring router is set in advance as thenetwork layer processing unit in this router (step S3005) such that thereceiving targets of all the VCs within the VP for datagram transfer areset in the L2 routing table in advance.

Then, the second stage router which received the datagram destined tosome unregistered sub-net through the VC other than the default VC fromthe first stage router (step S3006) recognizes that the previous stagerouter wishes to use that VC as the dedicated VC destined to thedestination sub-net of the received datagram, as this datagram isreceived from the VC other than the default VC.

Then, unless this second stage router is the final stage router of thisdedicated VC (step S3007 NO), this second stage router looks up therouting table in this router to check the next stage router (S3009),captures one arbitrary unused VC to the next stage router other than thedefault VC within the VP connected to the next stage router andtransmits the datagram destined to that sub-net through that VC (stepS3010), while this VC between the second stage router and the thirdstage router is directly connected at the ATM layer with the VC betweenthe first stage router and the second stage router by an appropriatesetting in the L2 routing table (step S3011).

The third and subsequent intermediate stage routers also operatesimilarly as the second stage router.

When the destination sub-net of the datagram received from the unused VCis a sub-net for which the direct delivery is supported by this router,the router recognizes that it is the final stage router to which thededicated VC is destined, so that this VC is registered as the bypasspipe destined to this router, and the transfer target of the receiveddatagram is set to be the network layer processing unit in this router(step S3008).

By means of these operations, it is possible to construct the bypasspipe environment without using any bypass pipe set up request message.In this procedure, the bypass pipe is constructed only at the route inwhich the datagram to be transmitted actually exists, so that there isan advantage that a wasteful set up operation for a bypass pipe which isactually not going to be used can be eliminated.

Next, with references to FIG. 42 to FIG. 48, the second bypass pipe setup/release procedure using no control message will be described.

The following description is based on an exemplary configuration asshown in FIG. 42 in which the ATM-LANs 603 have switches 604 (604a to604e) connecting the routers 601 (router-A and router-B) and theterminals 602 (host H1 and host H2) to the ATM-LANs 603, where theswitch 604a provides a VC (PVC) between the host HI and the router-A,the switches 604b and 604c provide a VC (PVC) between the router-A andthe router-B and the switches 604d and 604e provide a VC (PVC) betweenthe router-B and the host H2.

In this case, each terminal 602 has a configuration as shown in FIG. 43,which is basically similar to that of FIG. 9 and which comprises: an ATMlayer processing unit 621; and ATM cell-IP packet conversion unit 622connected with the ATM layer processing unit 621; an IP layer processingunit 623 connected with the ATM cell-IP packet conversion unit 622, anda VC management unit 624 and a destination management unit 627 connectedwith the IP layer processing unit 623, where the VC management unit 624includes a VC control unit 625 and a VC management table 626, while thedestination management unit 627 includes a destination control unit 628and a destination management table 629.

On the other hand, each router 601 has a configuration as shown in FIG.44, which comprises: an ATM layer processing unit 611 (corresponding tothe datalink layer switch unit 202 of FIG. 4); and ATM cell-IP packetconversion unit 612 (corresponding to the datalink layer-network layertranslation unit 203 of FIG. 4) connected with the ATM layer processingunit 611; an IP layer processing unit 613 (corresponding to the networklayer switch unit 204 and the network layer control unit 207 of FIG. 4)connected with the ATM cell-IP packet conversion unit 612; and a bypasspipe management unit 617 connected with the ATM layer processing unit611 and the IP layer processing unit 613 and a VC management unit 614connected with the IP layer processing unit 613 (corresponding to thethe datalink layer connection set up judgement unit 205 and the datalinklayer control unit 206 of FIG. 4), where the VC management unit 614includes a VC control unit 615 and a VC management table 616, while thebypass pipe management unit 617 includes a bypass pipe control unit 618and a bypass pipe management table 619.

Here, the switches 604a to 604e have route control tables with initialsettings as indicated in FIG. 45A to FIG. 45E, respectively, while thehost H1, the host H2, the router-A, and the router-B have the VCmanagement tables 616 with initial settings as indicated in FIG. 46A toFIG. 46D, respectively.

Now, with reference to the flow chart of FIG. 47, a procedure for thedata packet transmission by the transmission terminal 602 in this casewill be described first.

When data to be transmitted is generated (step S101), the destinationmanagement table 629 is referred to check if there exists an entrycorresponding to the destination IP address in the generated IP packet(S102). In a case a corresponding entry exists at the step S102, acorresponding I/F and a corresponding VPI/VCI are obtained from thedestination management table 629 (step S103). Then, the ATM cell isassembled according to a prescribed format (step S107) and the datapacket, i.e., the assembled ATM cell, is transmitted (step S108).

In a case a corresponding entry does not exist at the step S102, a nexthop is determined by referring to an IP routing table provided withinthe IP layer processing unit 623 (step S104), where the IP routing tableregisters the correspondence between the destination IP address and thenext hop IP address.

Then, the VC management table 626 is referred to obtain available I/Fand VPI/VCI corresponding to the next hop (step S105), and the statusfield in the VC management table 626 corresponding to the obtained I/Fand VPI/VCI is updated while the destination management table 629 isupdated by adding a new entry (step S106). Then, the ATM cell isassembled according to a prescribed format by adding the obtainedVPI/VCI (step S107) and the data packet, i.e., the assembled ATM cell,is transmitted (step S108).

Next, with reference to the flow chart of FIG. 48 a procedure for thedata packet handling by the router 601 in this case will be described.

When the data packet (ATM cell) is received (step S111), the bypass pipemanagement table 619 is referred by the ATM layer processing unit 611(step S112) to check if there exists a bypass pipe corresponding to theI/F and the VPI/VCI of the received ATM cell (step S113).

In a case the corresponding bypass pipe exists at the step S113, the ATMlevel exchange is executed at the ATM layer processing unit 611 (stepS114), and the data packet (ATM cell) is transmitted to the bypass pipeby only the ATM level processing (step S116).

In a case the corresponding bypass pipe does not exist at the step S113,the ATM cell is disassembled and given to the IP layer processing unit613, to determine a next hop according to the IP routing table providedtherein. Then, the VC management table 616 is referred to obtainavailable I/F and VPI/VCI corresponding to the next hop, according tothe IP address of the next hop. Then, the ATM cell is assembled again byadding the obtained VPI/VCI (step S115) and the data packet, i.e., theassembled ATM cell, is transmitted (step S116).

At the same time, the bypass pipe control unit 618 registers a set ofthe I/F and the VPI/VCI at times of reception and transmission of thatATM cell into the bypass pipe management table 619, to produce a newbypass pipe while updating the bypass pipe management table 619. Bymeans of this operation, the subsequent ATM cells having the sametransmission source and the same destination arriving to this routerafter this updating of the bypass pipe management table 619 can betransferred at high speed by only the ATM level processing at the ATMlayer processing unit 611.

In a case the VC cannot be obtained for some reasons such as a lack ofbandwidth or an occurrence of obstruction, the ATM cell loss will becaused. It is also possible to keep the subsequent ATM cells awaiting ina buffer (now shown) provided in the ATM layer processing unit 611 untilthe bypass pipe management table 619 is updated.

Here, the VC is basically bidirectional, so that when each of theterminal 602 and the router 601 obtains the VCID, if any unused VCID issecured at random, there is a possibility for the same VCID to besecured from both sides. In order to prevent such a case in which thesame VCID is secured from both sides, it is possible to determine inadvance a VCID of the VC given by a PVC that can be secured from a nodeon one side.

The deletion of the entry from the bypass pipe management table 619 canbe realized by a method using the ATM level message such as the OAM cellwhich is different from the control message at the network layer level,or by a method for deleting the entry according to a statisticalinformation such as a traffic on the bypass pipe.

Next, with references to FIG. 49 to FIG. 51, the third bypass pipe setup/release procedure using no control message will be described.

In the second procedure described above, the VCs of the same functionare setup between the terminal 602 and the router 601 as well as betweenthe routers 601. In this third procedure, the default Vc and thededicated VC are set up between the terminal 602 and the router 601 aswell as between the routers 601. Then, a sender who wishes to make theconventional IP level transfer of the data packet at the router 601utilizes the default VC for the data packet transmission, while a senderwho wishes to make the ATM level transfer of the data packet at therouter 601 as much as possible utilizes the dedicated VC for the datapacket transmission.

In this case, each terminal 602 has a configuration similar to thatshown in FIG. 43 described above, except that the VC management table626 in the VC management unit 624 has an internal configuration as shownin FIG. 49, which includes a default VC management table 6261 forregistering a VPI/VCI of a VC defined in advance as the default VC foreach VC connection target and an other VC management table 6262 forregistering a VPI/VCI of a VC other than the default VC. Similarly, eachrouter 601 has a configuration similar to that shown in FIG. 44described above, except that the VC management table 616 in the VCmanagement unit 614 has an internal configuration similar to that shownin FIG. 49, which includes a default VC management table 6161 forregistering a VPI/VCI of a VC defined in advance as the default VC foreach VC connection target and an other VC management table 6162 forregistering a VPI/VCI of a VC other than the default VC.

Now, with reference to the flow chart of FIG. 50, a procedure for thedata packet transmission by the transmission terminal 602 in this casewill be described first.

When data to be transmitted is generated (step S121), the destinationmanagement table 629 is referred to check if there exists an entrycorresponding to the destination IP address in the generated IP packet(S122). In a case a corresponding entry exists at the step S122, acorresponding I/F and a corresponding VPI/VCI are obtained from thedestination management table 629 (step S123). Then, the ATM cell isassembled according to a prescribed format (step S130) and the datapacket, i.e., the assembled ATM cell, is transmitted (step S131).

In a case a corresponding entry does not exist at the step S122, a nexthop is determined by referring to an IP routing table provided withinthe IP layer processing unit 623 (step S124), and whether the ATMtransfer is wished as much as possible or not is decided (step S125).

When it suffices to make the conventional IP level transfer (step S125NO), the default VC management table 6261 in the VC management table 626is referred to obtain I/F and VPI/VCI corresponding to the next hop(step S128), and the destination management table 629 is updated (stepS129). Then, the ATM cell is assembled according to a prescribed format(step S130) and the data packet, i.e., the assembled ATM cell, istransmitted (step S131).

On the other hand, when it is wished to make the ATM level transfer asmuch as possible (step S125 YES), the other VC management table 6262 inthe VC management table 626 is referred to obtain available I/F andVPI/VCI corresponding to the next hop (step S126), and the other VCmanagement table 6262 and the destination management table 629 areupdated (step S127). Then, the ATM cell is assembled according to aprescribed format (step S130) and the data packet, i.e., the assembledATM cell, is transmitted (step S131).

Next, with reference to the flow chart of FIG. 51 a procedure for thedata packet handling by the router 601 in this case will be described.

When the data packet (ATM cell) is received (step S141), the bypass pipemanagement table 619 is referred to check if there exists a bypass pipecorresponding to the I/F and the VPI/VCI of the received ATM cell (stepS142).

In a case the corresponding bypass pipe exists at the step S142, the ATMlevel exchange is executed at the ATM layer processing unit 611 (stepS143), and the data packet (ATM cell) is transmitted to the bypass pipeby only the ATM level processing (step S150).

In a case the corresponding bypass pipe does not exist at the step S142,the ATM cell is disassembled and given to the IP layer processing unit613 (step S144), and a next hop is determined according to the IProuting table provided in the IP layer processing unit 613 (step S145).

Then, when the received ATM cell is a cell transmitted from the defaultVC (step S146 YES), the default VC management table 6161 in the VCmanagement table 616 is referred to obtain I/F and VPI/VCI correspondingto the next hop, according to the IP address of the next hop (stepS147). Then, the ATM cell is assembled again by adding the obtainedVPI/VCI (step S149) and the data packet, i.e., the assembled ATM cell,is transmitted (step S150).

On the other hand, when the received ATM cell is a cell transmitted fromthe dedicated VC (step S146 NO), the other VC management table 6162 inthe VC management table 616 is referred to obtain available I/F andVPI/VCI corresponding to the next hop, according to the IP address ofthe next hop (step S148). Then, the ATM cell is assembled again byadding the obtained VPI/VCI (step S149) and the data packet, i.e., theassembled ATM cell, is transmitted (step S150).

At the same time, the bypass pipe control unit 618 registers a set ofthe I/F and the VPI/VCI at times of reception and transmission of thatATM cell into the bypass pipe management table 619, to produce a newbypass pipe while updating the bypass pipe management table 619. Bymeans of this operation, the subsequent ATM cells having the sametransmission source and the same destination arriving to this routerafter this updating of the bypass pipe management table 619 can betransferred at high speed by only the ATM level processing at the ATMlayer processing unit 611.

MULTI-POINT TO POINT BYPASS PIPE SET UP/RELEASE PROCEDURE

Next, the bypass pipe set up/release procedures for a multi-point topoint connection in this embodiment will be described in detail.

The following description is based on an exemplary configuration asshown in FIG. 52 in which the ATM-LANs 111 to 118 are inter-networked bythe routers 11A to 11F, where the ATM-LANs 111 to 118 have sub-net IDsequal to #1 to #8, respectively.

In this case, the operation of the node (router) 11A for transmittingthe bypass pipe set up request is the same as that described inconjunction with FIG. 23 above.

On the other hand, the next stage router 11B operates according to theflow chart of FIG. 53 as follows.

When the bypass pipe set up request message is received from the router11A (step S6005), the router 11B captures the VCI value of the dedicatedVC from the previous stage router 11A and sets the network layerprocessing unit of that router as the terminal point of that dedicatedVC (step S6006).

Then, the router 11B analyzes the terminal sub-net of the receivedbypass pipe set up request message (step S6007) to determine whether totransfer this message to the next stage router or not (step S6008).

In a case of transferring this message, whether the bypass pipe to theterminal sub-net has already been established or not is determined (stepS6009), and when the bypass pipe has already been established, thatdedicated VC is directly connected to that bypass pipe at the ATM layerlevel by an appropriate setting in the L2 routing table, so as to becomea multiplexing point for that dedicated VC (step S6010).

On the other hand, when the bypass pipe has not been established, therouting table is looked up to determine the next stage router (stepS6011), and the bypass pipe set up request is transferred to the nextstage router (step S6012). Then, the router 11B captures the VCI valueof the bypass pipe to the next stage router, and directly connects theVCI values of the bypass pipe and that dedicated VC at the ATM layerlevel by an appropriate setting in the L2 routing table (step S6013).

Here, in a course of the bypass pipe set up, especially when a number ofrouters to pass is numerous, it is possible to encounter a situation inwhich the VC directly connected at the ATM layer exists up to anintermediate stage router but it has not reached to the final stagerouter yet. In such a case, the L2 routing table in the router may havea setting in which the connection target of the VC in a process of beinggenerated is set to the network layer processing unit in that router.

By means of this, the datagram is transferred only by the ATM layer upto that router as the datagram can pass through the other routers up tothat router by the ATM layer processing alone, so that compared with thehop by hop datagram transfer, the high speed datagram transfer ispossible even during the bypass pipe set up process.

Also, in this case, the timing for switching the connection target ofthe VC from the network layer processing unit of the router to the nextstage VC, i.e., the timing for rewriting a header conversion table or aswitch table (L2 routing table) in the router, can be set to a time atwhich one packet has passed through that VC, it is possible to preventan occurrence of a packet destruction (a situation in which only a partof the packet is transferred to the router while the other part of thepacket is transferred to the next stage router via the bypass pipe) atthis switching timing. For example, in a case of carrying out the ATMcell assembling of the datagram by using the AAL (ATM Adaptation Layer)type 5, this switching timing can be learned from the user-user datafield of the ATM cell, so that it suffices to carry out the tablerewriting when this switching timing is recognized.

Next, a set up of a multi-point to point bypass pipe in a case in whicha number of ATM-LANs to be inter-networked has increased will bedescribed.

When the router 11E and the router 11F are activated, the router 11Eestablishes the default VC between the router 11B and this router 11E,while the router 11F establishes the default VC between the router 11Cand this router 11F, and the operation such as the routing informationexchange is carried out through these default VCs. By means of therouting information exchange, the routers 11E and 11F recognize theexistence of the router 11A at several hops ahead, and an establishmentof the bypass pipe to this router 11A is attempted, as in the stepsS3001 to S003 of FIG. 40 described above.

Actually, the router 11F recognizes the existence of the router 11B(sub-nets #2 and #5), the router 11A (sub-net #1), and the router 11E(sub-net #7) at several hops ahead according to the routing informationexchange, so that the router 11F can transmit a bypass pipe set uprequest message containing three set up requests for three bypass pipesto these routers 11B, 11A, and 11E, to the router 11C. The router 11Ecan also transmit the similar bypass pipe set up request message to therouter 11B.

In this case, when the bypass pipe set up request message for a bypasspipe in a direction from the router 11F to the router 11A is receivedfrom the router 11F, the router 11C operates as follows.

Here, as shown in FIG. 54, the router 11C already has a bypass pipe 131between the router 11A and this router 11C. Consequently, themultiplexing of the bypass pipes is carried out within the router 11C.In other words, the when the VC for the bypass pipe from the router 11Fis captured, the router 11C merges this VC to the bypass pipe 131 fromthe router 11C to the router 11A that has already been establishedearlier. Namely, the VC from the router 11F to the router 11A and the VCfrom the router processing unit in this router 11C to the router 11A areboth connected to the bypass pipe 131 from the router 11C to the router11A by using a table in the add/drop and header conversion unit withinthis router 11C (or a switch table in a case of a multi-port router).

Similarly, when the bypass pipe set up request message for a bypass pipein a direction from the router 11E to the router 11A is received fromthe router 11E, the router 11B utilizes the bypass pipe 131 to therouter 11A that has already been established in this router 11B, bymerging the VC for the bypass pipe from the router 11E to the bypasspipe 131 by an appropriate setting of a table in the add/drop and headerconversion unit within this router 11B (or a switch table in a case of amulti-port router), such that the datagram from the router 11E can reachto the router 11A by only the ATM layer processing.

Thus, in this case, as shown in FIG. 55, the bypass pipes from therouter processing units in the routers 11E and 11F are merged at therouter 11B to effectively form a spanning tree with the router 11A as aroot and the other routers as nodes.

Hence, the multi-point to point connection obtained in this procedure isobtained by the merging of the connections in the routers, and not by ause of a multi-point connection of the ATM-LAN. Consequently, thismulti-point to point ATM connection can be realized by the protocolamong the routers alone, and the datalink layer is not necessarilyrequired to have a function of a multi-point connection.

As described, in this procedure, it is possible to form the multi-pointto point ATM connection as shown in FIG. 55 in which each routerfunctions as a root (destination) and the other routers functions asleaves (start point).

Here, the cell flow from this multi-point to point ATM connection ismerged at each router functioning as a node, the multiplexing of thedatagram is necessary, and the following should be taken into account.

First, in a case of using the ALL type 3/4, a different MID (MultiplexIdentifier) should be assigned to the source of each datagram. By meansof this, it becomes possible for the router 11A to identify eachtransmission source.

Second, in a case of using the AAL type 5, the transmission sourceidentification at the cell level is impossible at the router 11A, sothat the add/drop function in the router or the ATM switch should beprovided with such a function that, in a given VC, until a transmissionof one AAL-PDU (datagram) is finished, the other PDUs are not allowed toflow into that given VC.

In the multi-point to point ATM connection obtained by this procedure,each router functions as a root (destination) and the branch points(nodes) of this multi-point to point ATM connection are located at therouters. In this manner, it becomes possible to realize the dedicated Vcwith a smaller number of VCs (or more specifically, a smaller number ofATM-LANs inter-networked to one ATM-LAN).

Thus, in this procedure, the spanning tree for the datagram transferwhich is generated by the routing protocol operating among the routersis directly realized by the multi-point to point connection formed bythe ATM connections. Note here that, within each ATM-LAN, each of thesemulti-point to point VCs is basically the point to point VC, which maybe a VC associated with QoS.

In this procedure, as a plurality of datagrams from a plurality oflocations are multiplexed into one VC at the router, there is apossibility for an overflow of the VC capacity or a cell loss within theATM switch to occur, in a case of the traffic concentration. Such anoverflow or a cell loss can be prevented by any of the followingmeasures.

(1) For the VC in which the congestion or the cell loss is likely tooccur, the relay of the cell to that VC by only the ATM layer processingcan be temporarily or partially interrupted and the routing to therouter processing unit is used instead.

(2) For the lower stream of the spanning tree (i.e., at a side closer tothe terminal point router), a larger bandwidth resource can be securedin advance compared with the upper stream.

(3) Basically, the cell loss occurs at the router which becomes a nodeof the spanning tree. Consequently, an ATM switch in such a router canbe selectively formed by a high performance switch capable of realizingthe lower cell loss rate compared with the ATM switch in the ATM-LAN.

It is to be noted that, besides those already mentioned above, manymodifications and variations of the above embodiments may be madewithout departing from the novel and advantageous features of thepresent invention. Accordingly, all such modifications and variationsare intended to be included within the scope of the appended claims.

What is claimed is:
 1. A network interconnection apparatus forconnecting at least two virtual connection-oriented logical networks,comprising:physical interface means for interfacing the logicalnetworks; memory means for storing a correspondence relationship betweena first virtual connection for receiving a packet from one logicalnetwork and a second virtual connection for transmitting the packet toanother logical network; first transfer means for determining a next hopnode by analyzing a destination node information at a network layerlevel, the destination node information being included in a packetreceived from a node belonging to said one logical network, forspecifying a virtual connection between the next hop node and thenetwork interconnection apparatus, and for transmitting the packet tothe next hop node belonging to said another logical network through thespecified virtual connection, when a correspondence relationship for avirtual connection used in receiving the packet is not stored in thememory means; reception means for receiving a control message containinginformation for registration of the correspondence relationship from atleast one of the node belonging to said one logical network and the nexthop node; registration means for registering the correspondencerelationship into the memory means according to the informationcontained in the control message; and second transfer means for carryingout a packet transfer without the network layer level processing,according to the correspondence relationship stored in said memorymeans, when the correspondence relationship for a virtual connectionused in receiving the packet is stored in said memory means.
 2. Theapparatus of claim 1, wherein the memory means also stores aninformation indicating whether a packet transfer by the first transfermeans is to be carried out with respect to a virtual connection used inreceiving the packet from said one logical network.
 3. The apparatus ofclaim 1, further comprising storage means for storing information foridentifying virtual connections formed between the networkinterconnection apparatus and other nodes,wherein the registration meansanalyzes the information contained in the control message, selects avirtual connection formed between another node and the networkinterconnection apparatus according to the information stored in thestorage means, and registers the correspondence relationship between theselected virtual connection and a virtual connection obtained byanalyzing the control message.
 4. The apparatus of claim 1, furthercomprising:transmission means for transmitting another control messagecontaining information for the registration of the correspondencerelationship to at least one of the node belonging to said one logicalnetwork and the next hop node; wherein the registration means also usesthe information contained in said another control message.
 5. A networksystem, comprising:a plurality of virtual connection-oriented logicalnetworks; a plurality of network nodes connected to the logicalnetworks, the nodes include network interconnection apparatusesinterconnecting the logical networks, each network interconnectionapparatus has a memory means for storing a correspondence relationshipbetween a virtual connection available for transmitting a packet fromone network node and a virtual connection available for transmitting thepacket to another network node, and each network interconnectionapparatus transfers a newly received packet without carrying out anetwork layer level analysis when a correspondence relationship for avirtual connection used in receiving the newly received packet is storedin the memory means, whereas each network interconnection apparatustransfers a newly received packet by carrying out the network layerlevel analysis when a correspondence relationship for a virtualconnection used in receiving the newly received packet is not stored inthe memory means; wherein each network interconnection apparatus has areception means and a transmission means for respectively receiving andtransmitting a control message containing an information for specifyingthe packet to be transmitted through the virtual connections, accordingto which each network interconnection apparatus registers thecorrespondence relationship in the memory means via a registrationmeans.
 6. A network interconnection apparatus, comprising:at least oneinterface configured to receive and to transmit a packet through avirtual connection; a memory configured to store a correspondencerelationship between a first virtual connection to be used in receivinga packet with a specified destination address from a first nodebelonging to one logical network and a second virtual connection to beused in transmitting the packet with the specified destination addressto a second node belonging to another logical network; a first transferunit configured to determine the second node by analyzing a destinationnode information at a network layer level, the destination nodeinformation being included in a packet received from the first node, soas to specify a virtual connection between the second node and thenetwork interconnection apparatus, and to transmit the packet to thesecond node through the specified virtual connection, when acorrespondence relationship for a virtual connection used in receivingthe packet is not stored in the memory; a reception unit configured toreceive a control message which includes information for registration ofthe correspondence relationship from at least one of the first node andthe second node; a registration unit configured to register thecorrespondence relationship into the memory according to the informationincluded in the control message; and a second transfer unit configuredto transfer a packet received through the first virtual connection tothe second virtual connection without using the network layer levelprocessing, according to the correspondence relationship stored in thememory, when the correspondence relationship for a virtual connectionused in receiving the packet is stored in the memory.
 7. The apparatusof claim 6, further comprising:a transmission unit configured totransmit another control message containing information for theregistration of the correspondence relationship to at least one of thefirst and second nodes; and wherein the registration unit also uses theinformation contained in said another control message.
 8. The apparatusof claim 7, wherein the transmission unit transmits said another controlmessage according to statistical information regarding a transfer of thepacket to be transferred by the network interconnection apparatus. 9.The apparatus of claim 7, wherein the transmission unit transmits saidanother control message when the network interconnection apparatusreceives the packet to be transferred from the first node to the secondnode.
 10. The apparatus of claim 7, wherein each control messagecontains an identification information for one of the first and secondvirtual connection, the identification information being unique in eachlogical network, and an information for specifying a destination addressof the packet to be transmitted through said one of the first and secondvirtual connection.
 11. A method of packet transfer, comprising thesteps of:receiving a control message from at least one of a first nodebelonging to one logical network and a second node belonging to anotherlogical network; registering, in a memory, a correspondence relationshipbetween a first virtual connection available for receiving a packet witha specified destination address from the first node belonging to the onelogical network and a second virtual connection available fortransmitting the packet with the specified destination address to thesecond node belonging to the another logical network, according toinformation for specifying a destination address of a packet to betransferred through the first virtual connection and the second virtualconnection, at least a part of the information being included in thecontrol message received; transferring a packet received through thefirst virtual connection to the second virtual connection withoutcarrying out a network layer level analysis, according to thecorrespondence relationship stored in the memory; and transferring apacket received from the first node to the second node by carrying outthe network layer level analysis, when a correspondence relationship fora virtual connection used in receiving the packet is not stored in thememory.
 12. The method of claim 11, wherein the storing step stores thecorrespondence relationship according to an identification informationfor a desired virtual connection available for transmitting the packetover different logical networks without the network layer levelanalysis, the identification information being contained in a controlmessage received from at least one of the first and second nodes. 13.The method of claim 11, further comprising the step of:deleting thecorrespondence relationship from the memory when the control message isnot received for a predetermined period.
 14. The method of claim 11,further comprising the step of:deleting the correspondence relationshipfrom the memory when a delete control message is received from at leastone of the first and second nodes.
 15. The method of claim 11, furthercomprising the step of:deleting the correspondence relationship from thememory when the packet is not received through the first virtualconnection for a predetermined period.
 16. The method of claim 11,wherein the control message also contains an identification informationfor one of the first and second virtual connection, the identificationinformation being unique in each logical network, and the controlmessage being received through a virtual connection different from thefirst and second virtual connections.
 17. The method of claim 11,wherein the control message is a setup message for setting up one of thefirst and second virtual connections.
 18. The method of claim 11,wherein the control message is received through at least one of thefirst and second virtual connections.
 19. The method of claim 11,further comprising the step of:setting up at least one of the first andsecond virtual connection before storing the correspondencerelationship.
 20. A network interconnection apparatus for connecting atleast two virtual connection-oriented logical networks, comprising:amemory configured to store a correspondence relationship between a firstvirtual connection for receiving a packet from one logical network and asecond virtual connection for transmitting the packet to another logicalnetwork; a first transfer unit configured to determine a next hop nodeby analyzing a destination node information at a network layer level,the destination node information being included in a packet receivedfrom a node belonging to said one logical network, so as to specify avirtual connection between the next hop node and the networkinterconnection apparatus, said first transfer unit configured totransmit the packet to the next hop node belonging to said anotherlogical network through the specified virtual connection, when acorrespondence relationship for a virtual connection used in receivingthe packet is not stored in the memory; a reception unit configured toreceive a control message containing information for registration of thecorrespondence relationship from at least one of the node belonging tosaid one logical network and the next hop node; a registration unitconfigured to register the correspondence relationship into the memoryaccording to the information contained in the control message; and asecond transfer unit configured to carry out a packet transfer withoutthe network layer level processing, according to the correspondencerelationship stored in the memory, when the correspondence relationshipfor a virtual connection used in receiving the packet is stored in thememory.
 21. A network interconnection apparatus, comprising:means forstoring a correspondence relationship between a first virtual connectionto be used in receiving a packet with a specified destination addressfrom a first node belonging to one logical network and a second virtualconnection to be used in transmitting the packet with the specifieddestination address to a second node belonging to another logicalnetwork; means for determining the second node by analyzing adestination node information at a network layer level, the destinationnode information being included in a packet received from the firstnode, so as to specify a virtual connection between the second node andthe network interconnection apparatus, and for transmitting the packetto the second node through the specified virtual connection, when acorrespondence relationship for a virtual connection used in receivingthe packet is not stored in the storing means; means for receiving acontrol message which includes information for registration of thecorrespondence relationship from at least one of the first node and thesecond node; means for registering the correspondence relationship intothe storing means according to the information included in the controlmessage; and means for transferring a packet received through the firstvirtual connection to the second virtual connection without using thenetwork layer level processing, according to the correspondencerelationship stored in the storing means, when the correspondencerelationship for a virtual connection used in receiving the packet isstored in the storing means.
 22. A method of packet transfer, comprisingthe steps of:receiving a control message from at least one of onelogical network and another logical network; storing, in a memory, acorrespondence relationship between a first virtual connection forreceiving a packet from said one logical network and a second virtualconnection for transmitting the packet to said another logical networkaccording to information included in the control message received;determining a next hop node by analyzing a destination node informationat a network layer level, the destination node information beingincluded in a packet received from a node belonging to said one logicalnetwork, specifying a virtual connection to the next hop node, andtransmitting the packet to the next hop node belonging to said anotherlogical network through the specified virtual connection, when acorrespondence relationship for a virtual connection used in receivingthe packet is not stored in the memory; and carrying out a packettransfer without the network layer level processing, according to thecorrespondence relationship stored in the memory, when thecorrespondence relationship for a virtual connection used in receivingthe packet is stored in the memory.